Thank you to Milosz for recommending Desktop Drapes. He's the developer, so if you like it you should let him know over at his site. It's a good opportunity to learn more about the open source community in the wonderful oasis of Ann Arbor in the desert of Michigan.
Desktop Drapes is a nifty utility used to randomize your desktop wallpaper. You add a couple pictures to the list, tell it how long to set them for, and you'll get some instant freshness to your desktop.
Open up a Terminal (or do it the Synaptic way) and type the following:
sudo apt-get install drapes