If you like variation in your desktop backgrounds and you're into a bit of 60's psychedelia then you should take a look at Google's Top Draw.
In the Menubar Viewer, you have a certain amount of control over how the desktop backgrounds are displayed in terms of color (using the pallet) and the shapes of the design i.e. rectangles, circles, squares etc. The great thing is that every design is unique and you can let Top Draw roll through backgrounds automatically so that every time you revert to your desktop, you get a completely new unique design.
Top Draw is typically Google - neat, lightweight and mightily impressive in the uniqueness of the design and backgrounds it comes-up with.