There's a lot of awesome commercial free use stuff up on the Nasa site. Great for all sorts - phone backgrounds, desktop/laptop wallpapers and likely for my new interest of cartography.

http://www.nasa.gov/multimedia/imagegallery/index.html

The ones I like the most are from the JPL - the awesome enhanced shots of space. There's a wealth of shots of their project equipment etc too.

Usage guidelines are here for quick reference;

http://www.nasa.gov/audience/formedi...l#.VS0GyC5fc5w