NASAPrize - NASA Centennial Challenges
nasamici - NASA's Minority Innovation Challenges Institute, managed by Florida A&M, seeks to train minority undergrads across the US to compete in NASA tech challenges.
nasa_ntl - NASA Tournament Lab - http://www.topcoder.com/home/ntl
Regolith Excavation Challenge
Regolith_Chal - Regolith Excavation Challenge (a Centennial Challenge)
paulsrobotics - Serving all your robotic needs - http://www.paulsrobotics.com/
grncheese - Ellen Crain - Building an entry for the 2009 Regolith Excavation Challenge
Space Elevator Games
segames - Ted Semon - Mojave, California - Official tweets from the Space Elevator Games
LaserMotive - Laser Power Beaming Competition team
USST - UofS Space Team
#SEGames - a hashtag used during the games
#TPNASA - another hashtag used during the games
Northrop Grumman Lunar Lander Challenge
NGLLC09 - LunarLanderChallenge - Northrop Grumman Lunar Lander Challenge, presented by X PRIZE, and prize money from NASA
bonnova - design . innovation . lunar lander challenge team http://www.bonnova.com/
mastenspace - Masten Space Systems
colinake - Recent Georgia Tech Grad (09) working at GTRI and Masten Space Systems. Join me for musings on life, space, technology, and whatever.
wikkit - Ben Brockert - I moved from Iowa to the Mojave Desert to be a rocket scientist.
dmasten - Dave Masten
rocketrepreneur - Jonathan A. Goff - Your typical mild-mannered rocket engineer, dad, and entrepreneur
AltiusSpace - Official Twitter account for Altius Space Machines
mmealling - Michael Mealling (Masten Space Systems)
unrocket - Paul Breed - Unreasonable Rocket
ArmadilloGadget - Phil Eaton - http://www.armadilloaerospace.com/
id_aa_carmack - Founder and technical director of Id Software (Wolfenstein, Doom, Quake, Rage) and Armadillo Aerospace
Google Lunar X PRIZE
glxp - Google Lunar X PRIZE
Odyssey_Moon - Odyssey Moon, Google Lunar X PRIZE team and commercial space venture
Bob_Richards - Space entrepreneur. Orphan of Apollo. Founder of International Space
University, Singularity University and Google Lunar X PRIZE competitor Odyssey Moon Ltd.
whitelabelspace - White Label Space (Google Lunar X PRIZE team) LunarX_EU - earlier White Label Space twitter
SteveAllen - CEO Clearer Partners rapid innovation & technology group. Team Lead for White Label Space a Google Lunar X-PRIZE contender
lunarnumbat - Our goal is to put a Linux powered robotic Australian marsupial on the moon, come join us!
rcspacepioneers - Rocket City Space Pioneers
interorbital - Randa Milliron - CEO/CoFounder, Interorbital Systems and Trans Lunar Research SynergyMoon - Google Lunar XPRIZE entrant Team Synergy Moon
OmegaEnvoy - We are the Florida Team competing in the Google Lunar X PRIZE. We are students, engineers, entrepreneurs, and space geeks: Join us on our awesome adventure!
oe_rover - Omega Envoy Rover - I'm the Omega Envoy Rover being built to go to the moon to win the 30 million dollar Google Lunar X PRIZE. Follow me to the moon!
ARCAspace - Asociatia Romana pentru Cosmonautica si Aeronautica (ARCA) este o organizatie non-guvernamentala, lider national in domeniul cercetarii aerospatiale.
NextGiantLeap - Michael Joyce - A Google Lunar X PRIZE team
teamFREDNET - Team FREDNET is an open source and open participation competitor in the Google Lunar X PRIZE
csete - Alexandru Csete - I work with space, communications, video processing and related technologies. I blog for GLXP @teamfrednet.
jeffkrukin - NewSpace Business Development consultant, speaker, and writer
SoldTheMoon - David Gump - http://www.astrobotictech.com/ - private-sector space exploration
Team_Selenokhod - Russian Google Lunar X PRIZE Team
openmoon - c-base Open Moon - Google X-Prize Competitor
PuliSpace - Puli Space Technologies is a Hungary based team aiming to land a self-made rover on the Moon. Follow us and get to know how the Puli rockets into space.
Moon_Ex - Moon Express, Inc. - MoonEx is a privately funded lunar transportation and data services company establishing new avenues for commercial space activities beyond Earth orbit.
astrobotic - Astrobotic Tech
spacemeta - SPACEMETA if the First AERO SPACE Company created in Brasil that will launch a Mission to the Moon.
teamspaceil - Team Space Il
teamindus - An idea whose time has come!
TeamSelene - Shanghai http://www.seleneteam.com
bcnmoonteam - Barcelona Moon Team
TeamJURBAN - Juxtopia Urban Robotics Brilliant Application National program trains undeserved students 2 build autonomous robotic systems that have impact in their community
lunarlionPSU - Penn State is competing in a global race to land and operate a robotic spacecraft on the Moon by 2015. We are…the Penn State Lunar Lion X Prize Team.
nprize - Paul Dear
NebulaAerospace - News from Nebula Aerospace (N-Prize team)
fineri - Iain Finer - Ametuer rocket engineer, aspiring song writer and musician.Just trying to live the dream.
ValkyrieFed - The Valkyrie Federation is a canadian (Quebec) entreprise, which has the goal of space exploration, and the lastest team on the N-Prize!
thomasspacecorp - Thomas Space Corp
TeamPrometheus - Advocates of the New Space Frontier
Astronaut Glove Challenge
pkhomer - http://www.flagsuit.com/ - Astronaut Glove Guy
X PRIZE Foundation
StarryBrit -Alex Hall - Stargazing since I was a child, always wanted to go..now as Sr Director of the Google Lunar X PRIZE, I can do it virtually through our amazing teams!
alias_amanda - Amanda Stiles - Space maven, website designer, crowdsourcing evangelist, and engineer of the entrepreneurial variety.
ChandaGo -Chanda Gonzales - Education Manager for Google Lunar X PRIZE
GLXPFeeds - Google Lunar X PRIZE - Feeds and news related to the Google Lunar X PRIZE. You can follow a human at @glxp
PeterDiamandis - Peter Diamandis
AnoushehAnsari - http://www.anoushehansari.com
genomics_xprize - A $10 million prize to the first team to successfully sequence 100 human genomes in 10 days
i_2_i - 2 days at the United Nations that will change your world. June 8 + 9. NYC. How WILL you innovate in today's economy?
progautoxp - The official Progressive Automotive X PRIZE Twitter
HealthXPRIZE - Developing a $10M+ X PRIZE to fix health care
xprize - Radical Breakthroughs for the benefit of humanity
OilCleanupXPF - $1.4 Million competition to inspire new innovative solutions that will speed cleaning up seawater surface oil resulting from spillage from ocean platforms.
ConradAwards - Enabling young minds to connect education, innovation, and entrepreneurship.
inventioneer - nancy conrad - Chairman of Conrad Foundation
sedsusa - SEDS - The world's only student run space organization!
FIRSTAtlanta09 - FIRST Championship 2009 in Atlanta, Georgia
firstforge - First Forge is the online community for sharing software among the FIRST Robotics competition teams
firstlegoleague - Behind-the-scenes info from FIRST HQ
FRCTeams - Director of First Robotics Competition at FIRST
FTCTeams - Updates, news and info about the FIRST Tech Challenge and the 2010-2011 game GET OVER IT!
WPI_Robotics - The WPI Robotics Resource Center runs lots of robot events and competition teams!
astrosociety - American Astronautical Society (listed here because of their CanSat competition coverage)
MoonBots - MoonBots: A Google Lunar X PRIZE LEGO® MINDSTORMS® Challenge
RWIWChallenge - NASA design challenge for upper school students.
RASCAL2011 - RASC-AL: REVOLUTIONARY AEROSPACE SYSTEMS CONCEPTS ACADEMIC LINKAGE
MOONBUGGYRACE - NASA's 17th annual Great Moonbuggy Race, April 9-10, 2010
SLI_1MILEHIGH - Rockets away! NASA's Student Launch Projects, April 15-18, 2010
Lunabotics - NASA Lunabotics - Kennedy Space Center
AlabamaLunabot - We are the University of Alabama Lunabotics Engineering Team. We design a robot to compete every year at NASA's Regolith Excavating Challenge.
RocketContest - The Aerospace Industries Association's Team America Rocketry Challenge is the world's largest rocket contest for middle & high school teams!
cswiki - Commercial Space Wiki (Ken Davidian)
richardbranson - Richard Branson (Chairman of Virgin Group)
rocketshadow - Aleta Jackson - I build rockets & rocket powered vehicles
rclague - Randall Clague
ikluft - Ian Kluft, Software Engineer and Commercial Pilot/Flight Instructor
Spaceport_NM - Spaceport America in New Mexico
ISPCS - International Symposium for Personal and Commercial Spaceflight
SpaceX_Media - cassie kloberdanz
ElonMusk - "I'm the genuine ElonMusk." muskfoundation.org teslamotors.com spacex.com solarcity.com paypal southafrica mars tolkien x.com blastar zip2 tosca kimb
SpaceX - Official Twitter for SpaceX, the Future of Space Travel. We design, build and launch the rockets and spacecraft that are revolutionizing space transportation.
XCORAero - XCOR Aerospace is a developer of safe, reliable and reusable rocket powered vehicles and propulsion systems.
mlaine - LiftPort - Building the Elevator to Space. Company Motto = "Change the world, or go home!" Author, Speaker, Consultant, Teacher, Venture Capitalist
ec_anderson - Eric Anderson, CEO of Space Adventures, serial entrepeneur.
spaceadventures - The world’s premier private space exploration company.
edyson - Internet court jEsther
robinsnelson - Robin Snelson - looking for a few good rockets
Virgin_Galactic - The world's first commercial spaceline.
Frank4 - Frank Taylor - Google Earth Blogger and sailor. Also read TahinaExpedition.com
gearth - Google Earth - Grab Google Earth and the Google Pack here
GoogleMoon - Something truly out of this world is coming, you WILL want to follow us...Promise. Clue - Facebook, Twitter & The Moon
digitalearth - All of the latest news about Google Earth, Virtual Earth, Google Maps, etc.
spaceangels - Space Angels Network - Premier source of aerospace dealflow for investors and of early-stage capital for aerospace
burtonlee - www.linkedin.com/in/burtonlee
StephenFleming - Academic VC, professional investor, amateur rocketeer
4frontiers - 4Frontiers Corporation is an emerging space commerce company focused on the settlement of Mars.
the2suit - the (unofficial) real 2suit - as seen on History Channel The Universe - humanity is colonizing the universe in 2s ... Zero-G or Earth ultimate geek gadget FLY!
8C_Project - 8thContinentProject - Colorado School of Mines - The 8th Continent Project connects start-ups built on space technology – in energy, medicine, GPS, materials. We call it Space 2.0.
RichardGarriott - Computer Gaming Pioneer and Private Astronaut (1st 2nd Generation)
gozerog - a privately held space entertainment and tourism company http://www.gozerog.com/
nextstepinspace - Show Your Support for Commercial SpaceFlight!
NewSpaceNews - http://spacefrontier.org/ - follow NewSpace News to stay informed about developments in the exciting entrepreneurial space arena! *Sponsored by SpaceIsle.com*
NewSpaceCon - NewSpace Conference - @SpaceFrontier's annual Conference highlights NASA-private cooperation, business of #NewSpace, & frontier enabling tech of tomorrow. NS11: July 28-31 in CA. http://newspace2011.spacefrontier.org/
suborbi_science - Dedicated to realizing the potential of next-gen suborbital spaceflight for research and education.
NSRC2011 - NSRC is the Next Generation Suborbital Researcher's Conference--THE suborbital meeting for researchers & educators. Come to Orlando to learn, network, & speak.
NSRC2013 - The Next Generation Suborbital Researcher's Conference is THE suborbital mtg for researchers & educators. Be in Palo Alto Feb 27-29-- Learn, Network & Present!
OrbitalSciences - Orbital Sciences Corporation
TeachersInSpace - The Teachers in Space program wants to put a thousand astronaut teachers into American classrooms, within the next decade.
RRLeague - Rocket Racing League will transform 21st Century racing as we know it. Think NASCAR in the sky using rocket-powered aircraft flown by top pilots and astronauts.
rpournelle - Rich Pournelle - Senior Vice-President of Business Development @Nanoracks. We can get your payload to the International Space Station.
Nanoracks - Entrepreneurial space company with permanent hardware in orbit. Commercial contributor to the U.S. National Lab on Space Station. Space 4 Everyone!
CommercialCrew - We're about NASA's Commercial Crew to ISS program and everything related to commercial companies putting astronauts and crew in space.
Pomerantz - Will Pomerantz, Vice President for Special Projects at Virgin Galactic. Former head of the $30 million Google Lunar X PRIZE. Opinions here are my own, not my employer's.
nickyjor - aerospace eng,space lover, tech girl,dancer,pilot!! social media learner, fashion enthusiast,wine lover and well..I am simply a person who loves life
stratolaunch - http://stratolaunch.com
UPAerospace - UP Aerospace Corporation, a space launch and test flight services provider, was incorporated in 2004 to offer world class access to space.
PlanetaryRsrcs - Planetary Resources - New space venture with mission to expand Earth's resource base & help ensure humanity’s prosperity.
tvaerospace - Terminal Velocity - Offering atmospheric reentry services to enhance safety and promote space utilization - http://www.tvaero.com
U. S. Human Space Flight Plans Committee
NASA_HSF - The Committee will conduct an independent review of ongoing U.S. human space flight plans and programs, as well as alternatives.
AstroDude - Leroy Chiao - Astronaut and more...
jeff_foust - Jeff Foust, Space industry analyst, writer, blogger, baseball fan
HobbySpacer - Clark Lindsey, Publisher and editor of HobbySpace.com and SpaceTransport News.com
SpaceShow - Dr. David Livingston, Host of The Space Show talk show
spacehack - a directory of ways to participate in space exploration. interact + connect with the space community.
milesobrien - Miles Obrien, freelance journalist
SpaceflightNow - Spaceflight Now
NASAWatch - NASA Watch
KeithCowing - Keith Cowing (NASA Watch, also see http://www.cowing.com/)
andrewchaikin - Andrew Chaikin
Free_Space - Irene Klotz blogs about what's happening off Earth
bencredible - Alpha nerd at Innovating Media and TechnologyEvangelist.com
SpaceFellowship - The International Space Fellowship (ISF) is an international news and information network dedicated to the development of the aerospace industry.
b0yle - Alan Boyle (MSNBC/Cosmic Log)
flspacereport - Edward Ellegood
xenijardin - Curator of Internet Esoterica, Anomalies, and Curiosities. BB co-editor, Boing Boing Video host/exec producer. http://tv.boingboing.net/
fitzwillie - Editor of GeekDad.com. That says a lot right there.
MichaelBelfiore - Michael Belfiore - Space & technology writer for Popular Science, Popular Mechanics, HarperCollins, and advanced technology companies.
flighthyperbola - Rob Coppinger is a recovering powerpoint user and engineer who mistakenly thought journalism was more glamorous than production engineering
UniGalactic - SpaceTravel Magazine - UniGalactic is a Unique Print Magazine Covering Space Tourism as well as Space Travel and Exploration Industries.
spacecom - Managing editor, Parabolicarc.com. Communications specialist. Have something to say. Let me help you say it.
robertpearlman - Editor, collectSPACE.com
collectspace - The Source for Space History & Artifacts
spaceteam - Fla Today Space Team - Live space updates at The Flame Trench, honored last year as the best beat reporting on the web.
SpaceKSCBlog - Stephen C. Smith is a member of the National Space Club, the National Space Society, and the Flight Test Historical Foundation. http://www.spaceksc.com/
Doug_Comstock - Director of NASA Innovative Partnerships Program (includes Centennial Challenges, FAST, SBIRs, etc)
NASA_Technology - The official Twitter account for NASA's Office of the Chief Technologist
worden - Pete Worden (NASA Ames Director)
waynehale - Wayne Hale (Former Flight Director)
gtwhitesides - George Whitesides
LADEE_NASA - Lunar Atmosphere and Dust Environment Explorer
LCROSS_NASA - NASA mission to explore the Moon and see if there is water ice near one of the lunar poles!
NASA_Ames_Web - NASA Ames Web
NASA_Wallops - NASA Wallops, Wallops Island, VA
PharmaSat - The PharmaSat experiment and flight system are designed to measure the influence of microgravity upon yeast resistance to an antifungal agent.
NASA_Greenspace - NASA_Greenspace
NLSI - NASA Lunar Science - Moon science rocks
NASAGoddard - Check out all the latest in NASA Goddard news and video!
Astro_Mike - Mike Massimino - NASA astronaut, mission specialist for STS-125 (Hubble Telescope servicing mission)
SPOTScott - Scott Parazynski - Drawn to explore high places, via spacecraft, aircraft and even on foot!
NewHorizons2015 - The First Space Mission to Explore Planet Pluto and the Kuiper Belt
flymetothemoon - NASA manager for LCROSS–NASA’s 1st mission back to the Moon, MoM/StepMoM, anthropologist, walker, chef, and BookBabe.
MarsRovers - Spirit and Oppy - Roaming the Red Planet on six wheels. The official mission Twitter of Spirit and Opportunity
jetlab - The latest news from the Jet Propulsion Laboratory. This Twitter is a service of SpaceLinks.net: http://spacelinks.net/
EarthObser - Earth Observatory from NASA
Lori_Garver - Deputy Administrator, NASA
ARTEMIS_NASA - We're two satellites on our way to the Moon to study space physics!
Bobby_Braun - Husband. Father. Aerospace Engineer. Professor. Term Bureaucrat.
NASA_commercial - News and updates from NASA's team focused on supporting the Emerging Commercial Space sector - NASA and Commercial Space
AMS_02 - AMS-02 the Alpha Magnetic Spectrometer high energy science experiment - Location: Outside ISS, among cosmic rays - ams02.org
ISS_NatLab - As the Nation's newest national laboratory, the ISS will strengthen relationships for the advancement of science, technology, engineering, and mathematics.
ISS_research - NASA's official source for research news from the International Space Station (ISS) - The world's laboratory in orbit.
NanoSailD - Deploy NASA's first solar sail leveraging work by MSFC approved under the SMD In-Space Propulsion Program
NASA_OOREOS - The O/OREOS (Organism/Organic Exposure to Orbital Stresses) nanosatellite contains an automated space laboratory with two astrobiology separate experiments
nasacrusr - NASA's Commercial Reusable Suborbital Research Program
nasa_eo - NASA images, stories, and discoveries about climate and the environment.
MorpheusLander - A vertical testbed vehicle at NASA Johnson Space Center
phalanx - Justin Kugler - Aerospace engineer at JSC, politics and space blogger. This is my personal account and all expressed opinions are my own.
isscasis - CASIS manages the International Space Station U.S. National Laboratory. Since 2011, our mission has been to maximize the utilization of the ISS NL.
ChallengeGov - The official Twitter account for Challenge.gov
tedprize - TED Prize
Prize4Life - Accelerate the discovery of a treatment and a cure for ALS (Lou Gehrig’s disease) by using powerful incentives to attract new people and new ideas.
http://twitter.com/greenflightchal - 2011 CAFE Green Flight Challenge - A pilot and builder interested in getting us all into more efficient atmospheric global travel. If we are going to survive, we have to get off the pavement
SpaceFrontier - Space Frontier Foundation -People dedicated to opening the space frontier to human settlement
kimbal - Kimbal Musk
isdc - The International Space Development Conference is the premier space activist conference. See http://isdc.nss.org/
nss- National Space Society
spaceelevator - Cheap reliable access to space.
ewalker - Elaine Walker - Bio EPO, Mars Institute
airshipventures - Zeppelin Tours of the San Francisco Bay Area
arielwaldman - Ariel Waldman - Digital Anthropologist. Founder of Spacehack.org; CupcakeCamp. Engadget columnist. Previous NASA program coordinator, Pownce community manager.
antifaev - Youthful engineer/entrepreneur with a special affinity for anything awesome.
InnosightInstit - a non-profit think tank that applies Clayton Christensen’s theories of disruptive innovation to the social sector. See our recently published books to the left.
revrev - Mike Fabio - Community Manager at Google Lunar X PRIZE; musician; nerd; no I will not fix your computer.
fedcity - Diane Murphy
MDRSupdates - MDRS Official Update - You can go to Mars, but you can never leave!
YurisNight - A global celebration marking the anniversary of manned spaceflight.
LunarPioneer - Joel Raupe - Principal Investigator, Lunar Pioneer Research Group; Promoting extended human activity on Earth's Moon
TEMPO3 - Sci-fi 2 sci-fact (Mars Society artificial gravity smallsat project)
TEDMED - Marc Hodosh - TEDMED 2009: OCTOBER 27-30 IN SAN DIEGO! CHECK OUT WWW.TEDMED.COM AND REGISTER TODAY!
shellymurray1 - Michelle Murray - FAA AST Experimental Permit Program Lead
willjwatson - William Watson - Executive Director, Space Frontier Foundation
SpaceFrontier - SpaceFrontierFound'n - People dedicated to opening the space frontier to human settlement
jamesmuncy - Space policy/business consultant
kdavidian - Ken Davidian - One Exciting Challenge After Another
brettalexander - Bretton Alexander
lorettahidalgo - Loretta Whitesides - Co-creator of Yuri's Night, Zero-G Flight Director, and passionate about bring people together to made a huge difference on our home planet...
flight0001 - Russ Dale - Writer, journalist, paleoecologist, scientist, urban farmer, chef, space enthusiast, actor, comedian, space 2.0 advocate and human (featured in the gonzo Russ Dale X-Prize Cup Interview, I might add).
makerfaire - Maker Faire Bay Area May 30-31 (The World's Largest DIY Festival)
Murphian - Ian Murphy - PR expert specializing in Aerospace, Technology and Science
neiltyson - Neil deGrasse Tyson - Astrophysicist, American Museum of Natural History. Author: "The Pluto Files" & "Death By Black Hole"; Host: PBS NOVA scienceNOW
digitalart - Jim Plaxco - A digital artist and photographer specializing in astronomical art and abstract art
SpaceSolarPower - Space solar power satellites will provide Earth with abundant, clean electric power.
moonrangerlaura - Space enthusiast; Works on a space telescope; Loves scifi/fantasy, travel, podcasts, fiber arts and of course people. Not officially speaking for anyone but me
Apollo11TheGame - iPhone Game developed by Decode Interactive in conjunction with NASA.
GwenGriffin - Houston and often Cocoa Beach
TeslaMotors - The official Tesla twitter
BadAstronomer - Phil Plait - Astronomer, author, skeptic, funny guy, writer
SGAC - Space Generation Advisory Council in support of the United Nations Programme on Space Applications
Moon4You - space instrument bringing the benefits of the Moon back to Earth
ad_astra2 - Erika Wagner - Cambridge, MA (blogging at MIT Giant Leaps)
therealBuzz - Buzz Aldrin, Astronaut, Apollo XI, Gemini 12, Doctorate from MIT in astronautics, married to Lois Aldrin for 21 years. Korean War veteran - fighter pilot of 66 missions
ac_charania - http://planetarydefense.blogspot.com/
wingod - Dennis Wingo
EVA_Interviews - Eva-Jane Lark - EVA is creator and host of EVA Interviews: The Business of the new Space Age™ (and in real life a VP and Investment Advisor at a major Canadian investment co)
Stratofox_Team - Stratofox Aerospace Tracking & Recovery Team - volunteer non-profit group assists with search and retrieval of high-altitude rockets and balloons
VisionRestore - Restore the Vision for Space Exploration and the rest of NASA
RocketRick - Rick Tumlinson - NewSpace Revolutionary, Space Frontier Foundation, Space Diver, Orbital Outfitters, Texas Space Alliance, EarthLight Institute, Led Mir team, speaker, writer
TEA_in_Space - The twitter account for #TEAParty members, #Republicans, & #Democrats who are genuinely interested & concerned with the U.S. #Space Program
spacevision2012 - http://spacevision.seds.org
orsoffice - Operationally Responsive Space Office
TiMEforTitan -Titan Mare Explorer, A finalist for the next NASA Discovery mission, TiME would perform the first direct inspection of a marine environment beyond Earth.
Moon - http://odysseymoon.com/ - Encouraging participation and collaboration among people interested in expanding humanity's social, legal and economic sphere to our sister world, the Moon.
TeamFREDNET - Team FREDNET is the open source competitor for the Google Lunar XPrize.
Astrogeology - http://astrogeology.usgs.gov/ - Astrogeology, alternatively known as planetary geology, is a planetary science discipline concerned with the geology of the celestial bodies such as the planets and their moons, asteroids, comets, and meteorites. The study of these rocks is similar to Earth-based geology.
Astronomy - For anyone intersted in Astronomy or Astrophotography.
Cosmology - Obsession of the Universe in its totality and humanity's place in it. Star seeking and theory, physics and awe.
LunarPioneers - http://lunarnetworks.blogspot.com/ - Lunar Pioneer is a long established "Society of Friends interested in exploration of the Moon," founded in 1977 as a private discussion club, the conversation intensified finally into an enterprise. Our goal remains unchanged: As the Rosetta Stone of the Solar System, Earth's Moon is also our Pier, our deep water port to our destiny.
Mars - http://martiansoil.com/ - All about the Planet Mars.
NASA - Encouraging participation and collaboration among people interested in NASA and space. News, views, and reviews to enlighten and inform.
SpaceFellowship - The International Space Fellowship (ISF) is an international news and information network dedicated to the development of the aerospace industry.
WaterRocket - You're a little Gyro Gearloose somehow and like to tinker with scientific stuff? This is your twibe!
geocaching - A place for geocachers to get together and see what other cachers are twittering about.
space - All things space & Earth & in between. NASA, commercial space, space industry, space geeks, dreamers, explorers. Welcome space tweeps!
Here's another, considerably longer and more comprehensive list that seems to have similar goals. It's too bad I didn't encounter it earlier. The coverage is somewhat different, since I'm going into prize and innovation topics that aren't specific to space, and this list covers a number of space areas I probably won't touch. I'd recommend checking the link below if you didn't find what you were looking for in the list above.
Twitter SpaceMeme - Space People, Missions, Agencies, Events ... - OnOrbit Colab Space
spacehack points out the following list of twitter sites from Star Stryder: astronomy-twitter-users. This list is mainly for astronomy sites of all sorts. The comments have more selections.
... and Ariel from spacehack also has the following list: Space-related web 2.0 accounts that are on my radar
... June 19 update: Follow active and former astronauts on Twitter - collectSPACE
... August 23 update: Top 50 Twitterrati for all of Space - Big on Good