Here's a fun space exploration program that's been around for a while, Celestia. Celestia allows you to zoom around the solar system and beyond with amazing images and accuracy. It supports Windows, Linux and Mac operating systems.
For those wanting to travel further out and for you sci-fi fans (and who isn't?), go to the "motherload" page there are deep space objects, galaxies and even Star Trek sites to be seen.
It's hours of entertainment for the whole family (at least the geeky ones).