Celestia is an awesome program that you can download for free. In Celestia, you can view 3D planets, comets, moons, stars and galaxies and you can travel faster than the speed of light. You can even control time! If that's not enough, you can even download more!
Celestia is similar to Google Earth in some ways, but different in others. In Google Earth, you can you onto the surface of a planet (Earth, Mars or Moon) in great detail, but in Celestia you can't. However, in Celestia, you can go way beyond the solar system and you can see the planets in great detail (but not the surface if you know what I mean).
Find out more info/download: http://www.shatters.net/celestia/