If you want something a bit more interesting than the standard desktop background for your display (or you use Ubuntu and you're just tired of BROWN!), you might want to take a look at what is available on the NASA HubbleSite web page. There is lots of interesting information, and more beautiful pictures than you can look at in one sitting. So far 80 of the pictures have been specially formatted and made available in a variety of resolutions to match most of the common display settings (and a lot of uncommon ones as well). You can download them from the Gallery/Wallpaper section.