Encyclopedia Astronautica is a good source for reference material about spacecraft, rockets, missiles, and rocket engines. Helpful features of the site include a chronology, space-related biographies not easily located elswhere and great graphics.
NASA Home Page
Up-to date information about astronomy and the space program. This site offers information for users from Kindergartens to astrophysicists.
"Access a vast amount of information about the space program, view live video from the space station or shuttle, view photos of planets, news releases, and read documentation about how the shuttle, satellites, and space probes operate. The site is operated by the government and all of the downloads are free."
Sea and Sky
Links to information about the solar system and constellations as well as deep sea creatures and aquariums.
Students for the Exploration and Development of Space provide information on astronomy, space sciences, aerospace and aeronautics.
Stephen Hawking's Universe
Hawking and other scientists explain many of the mysteries of the universe; web companion to PBS series.
"Sunrise, sunset tables, eclipses, data for major solar system bodies and bright stars, earth's seasons and dates."
Views of the Solar System
The solar system and its exploration, asteroids, comets, and meteorites can all be found on this multimedia site.