DisplayFusion: Multi-Monitor Wallpaper Software
DisplayFusion is a program for Windows 2000, XP, and Vista that makes it easy to manage wallpapers on multiple monitors. It works with dual monitors, triple monitors, or more. You have have one wallpaper span multiple monitors, or you can select different wallpapers for each monitor. It can pull photos from Flickr for use as wallpapers, or you can use your own photos on your computer.
DisplayFusion also provides a number of hotkeys or shotcuts to move and resize windows on multiple monitors.
The basic version of DisplayFusion is free. There is a pro version ($15) that includes more features such as timed wallpaper changes and fully customizable hotkeys.
Once you have installed DisplayFusion, it is time to find some multi-monitor wallpapers. You can start here, or you can do a Google search.