Freely Explore Space Through A Satellite's Silicon Eyes.
Google Maps Space is a free extension of Google Maps, available online, that provides a quasi-3D view of various planets and moons in the Earth's solar system and elsewhere in the galaxy. It also provides a view of the International Space Station, and provides the names and other notes (if applicable) at various landmarks on each of the planetary sites that it depicts.
Look Around, But You (And They) Can't Touch
It's an impressive technical feat that Google Maps Space has everything needed to display planets in a 3D form, that you can rotate in and zoom on and see the craters of by name. It does, however, suffer from a somewhat limited number of viewing options, mostly related to the difficulty that any spacecraft has today in retrieving a large number of long-distance photos. Perhaps the most interesting option is the interior tour of the International Space Station, but that suffers from interface problems, such as needing to click links to move around when in other Google Maps features, simply double-clicking a location will do.
A Brief Tour Of Space
As of this writing you can mostly visit planets within the solar system and their moons, and it is not likely that this will change quickly, as extraterrestrial footage is rare. However, Google Maps Space is worth trying even just to get a look at the International Space Station, complete with textual blurbs on how it works.