This one I had fun with. About 80,000+ faces. I made it in 3dsmax of course. Took about 2 hours to render. I edited it to include the full 1600x1200 for you guys that would like a kickass 3d Ubuntu wallpaper. Enjoy and more is on it's way.
I combined a grunge version of the Ubuntu logo with the Regal Blue wallpaper I found on InterfaceLift.
If you would like different logos, different sizes, different colors, or something else, please sound off in the comments.
As always, your comments and favorites inspire me to continue onwards.
EDIT: Added 1680x1050 version and Source XCF.
(NOTE: Sorry If I mis-categorized this. The only entry suitable was MAC & PC OS, so I put it there. There is no real Linux category there, and it's weird considering MACs are technically PCs. If you have a better suggestion for where I should put this, tell me in the comments.)