If you want a really good background then you should goto www.lighttek.com and download Talisman 2. I use it to make my desktop pretty! It also lets you change the way the Start button looks and a whole bunch of other stuff. If you want a wide range of themes then this is the program to get.

P.S. heres mine (well mines sterioscopic 3D cause I use my 3D glasses a lot but you get the idea)