NASA Jet Propulsion Laboratory - Great site for finding out about current space
missions. There is news, a calendar, missions to learn more about the solar system, and a site for kids.
The Astonomy Workshop - Java applets are used to let you
view rotation of planets and moons. You can also calculate orbits and the time it will take to travel to planets.
The Web Nebulae - Pictures of galaxies, clusters, and nebulae.
Beyond Einstein - NASA site on explorations of the structure of the universe
including the Big Bang, black holes, and dark energy.
Astronomy Basics- How to get started observing the stars
from Astonomy magazine.
At Home Astronomy - Hands-on astronomy experiments for the whole
family. The site is by the Space Sciences Laboratory at the University of California, Berkeley.