There are no simpsons wallpapers at n900wallpapers.com
What about making some?

We can make loopable ones with characters, with 2 desktops, 3 and 4 (it's kinda hard to make a REAL loopable wallpaper with 4 desktops...).

My idea is to blend some characters on a side using a color at background, making it "loop".

At wikipedia you can find great png with transparency, so it's a great start:

http://en.wikipedia.org/wiki/File:Ho...mpson_2006.png
http://en.wikipedia.org/wiki/File:Marge_Simpson.png
http://en.wikipedia.org/wiki/File:C-flanders.png
...
(you can find all here: http://en.wikipedia.org/wiki/List_of...n_The_Simpsons)

I mostly use 2 desktops, or 3.