The NASA multimedia library has some stunning images that would make interesting background pictures for many projects. There are pictures from various missions, spanning decades of space exploration.
For the most part, none of the images are copyrighted and may be used freely. Some of the artist concept drawings may be copyrighted, so it is best to read the image use guidline page for guidance.
A word of caution about image size.
Image size varies from small to very large, but the size of the images is clearly labeled. The background picture for my PF 2006 calendar submisson was 32MB. When opened in a jpeg viewer, the moon alone covered the entire monitor screen. Imagine that moon alone used as a backdrop rising behind some mountains or such. The possibilities are endless.
Enough talk.
The main index page.
http://www.nasa.gov/multimedia/imagegallery/index.html
Enjoy,
melamkish
