Here's a great post from Free Technology for Teachers on "8 Good Resources for Space Science Lessons." Resources include:
- Sloan Digital Sky Survey
- Google Earth (Did you know you can view tours of the moon? Simply select "Moon" from the planet menu in the Google Earth Toolbar! Mars, too! Ha! - who knew?)
- Google Sky
- NASA's interactive timeline and Planet Quest
- Gunn Interactive's Visualization of planets in orbit
- Amazing Space, and
- Microsoft's World Wide Telescope (my personal favorite, thanks to its educator's page)
The only link I might add is the the Smithsonian National Air and Space Museum. The sites above, though, are much easier to navigate & use.
Keep your head in the clouds!