Nico Hagen has posted two cool Blender wallpapers on his website. I quite like them as they are both very quiet and easy on the eye.
To celebrate this, I have changed my entire desktop theme to greys and combined with my newfound frenzy to clean up my desktop the result is quite good :)
You can download them in normal and wide-screen formats from Nico's website.
Update: if you want to see my new & improved clean desktop, look here. ;-)