Lifehacker has an awesome reader-fueled roundup of the best places to grab wallpaper specially designed to fit your glowing triptych (or wall) of unhealthy productivity. Mandolux snagged the top spot overwhelmingly, followed by InterfaceLIFT and that old-school favorite, DeviantART. There's more eye-exploding background heaven where that came from over at Lifehacker, which makes me kind of sad I only play on one monitor. If you've got your own tips, let us know about 'em, too. [Lifehacker, Images: last scionz/DeviantART, Mandolux]
If you are a loser running Windows (like me), try downloading UltraMon. It gives a lot of extra tools for navigating windows with multiple monitors, and it also allows you to set different desktop backgrounds for each monitor. Highly recommended.