If some of you awesome wallpaper designers would like a challenge, you could try your skills at making Windows Media Player backgrounds, if you felt like it.
I'm trying to come up with a method of switching them quickly and painlessly!
The element's optimal size would be 935px X 600px,
they need to be in both jpg and png format, (often the System32 dll requires a jpg while the SysWOW64 dll requires a png, don't ask me why!)
Matching theme colors or desktop wallpapers is cool but, try to keep the contextual elements from being masked by the 'album art' or the player controls, (as indicated by the red arrows)
Give it a go, if you feel like it; I'd be interested to see what you guys come up with!