jpl.nasa.govThe Jet Propulsion Laboratory is the lead U.S. center for robotic exploration of the solar system. JPL spacecraft have visited all known planets except Pluto (a Pluto mission is currently under study for the early part of the next decade).
setiathome.ssl.berkeley.eduCurrently the largest distributed computing effort with over 3 million users. Participate by running a program that downloads and analyzes radio telescope data in order to detect signs of alien contact.
planetary.orgThe Planetary Society is the largest and most effective nonprofit organization that promotes the exploration of space through education, advocacy, and innovative projects.