Allows you to run different wallpapers and screensavers on each monitor, plus gives you a taskbar on your secondary monitor that only shows the windows open on that monitor. And I *cough* don't have a keygen app for it either, so don't PM me if you need it!
http://www.realtimesoft.com/ultramon/
And just as well, here's some cool wallpapers to span dual monitors
http://www.mandolux.com/