I have a program that changes my wallpaper every 20 minutes and I have over 100 bitmaps and JPEGS of anime characters and scenes that I use. Everything from Rurouni Kenshin to Cowboy Bebop and Evangelion.
I usually use a random Kylie Minogue one. But recently I used a screen cap of Bruce Campbell in Evil Dead 2 right when he gives that insane face at the camera when all the furniture comes alive.