I change my desktop background fairly often. (Known as a 'wallpaper' way back in Windows 95, it is irritatingly referred to as a 'screensaver' quite a bit these days.) It goes from Doctor Who wallpapers to scenic views and cool photography, until I get bored with it and change it again. I've gone back to this photo a few times though, taken from a nice collection at wstaylor.net and - I think - included in Windows Vista.

What's yours?