NASA planet simulator

[HotSoup]

This is niffty. http://samadhi.jpl.nasa.gov/

[rwald]

Even better: http://www.shatters.net/celestia/

A downloadable real-time space simulator. You can view space from any point in the database (that is to say, any planet, satellite, asteroid, or star that the software knows of), and rotate everything in any direction you want. Very cool software.