The National Space Society
Space activist group focusing on legislation and commercialization. Headed by Buzz Aldrin.
The Planetary Society
Another group I'm a member of which leans more towards public education and non-government/commercial projects (such as SETI). Co-founded by the late Carl Sagan.
Search for Extra-Terrestrial life from home. A project run by SETI and The Planetary Society using screensavers on PC's throughout the world to search for alien radio signals.
Your ultimate store for astronaut autographs, spacecraft replicas, astronaut costumes, NASA logo clothes and gifts, and items flown in space.
A non-profit company working towards a privately funded lunar base. Founded by members of the Pacific Rocket Society
The First Millennial Foundation
A group founded to help save Earths environment and to colonize space. Founded by Marshall T. Savage, author of the book "The Millennial Project: Colonizing the galaxy in 8 easy steps.
Lunar Institute of Technology
Discussions and ideas on interstellar travel from the viewpoint of a futuristic college on the Moon.
The Case for Mars
Info on a conference on the exploration and colonization of Mars. Has lots of links to images of the Red Planet.
Extrasolar Planet Search
Info on extra-solar planets from the discoverers of 3 of the recent planets found.
The Harvard - Smithsonian Center For Astrophysics
Covers all the research projects being run browsable by topic.
The Near Earth Object (NEO) Program
NASA's program for finding near Earth asteroids and comets.
Lots and Lots of Space, Science and Celtic links.
Nine Eight Planets
Detailed descriptions and photos of the eight planets and many of their moons. Also includes many of the major asteroids and comets. Has the mass and size of all the bodies as well as interesting information such as where their name comes from.
Microsoft's test database of satellite imagery. Has a decent portion of the US and bits and pieces of other countries. You can spend hours scrolling around thru the images.