The European Homepage for The NASA/ESA Hubble Space Telescope hosts an impressive array of awesome (truly awe inspiring) images and wallpapers of our universe.

The images are formated in 1024×768, 1280×1024, 1600×1200.

My favorite part is the High Def videos that are available on the site. They have 720P and 1080P videos for download.
We are very excited about these kind of screen treats becoming more common on the net.