Like digital art? If you do, then you might want to check out the newly released Illusions theme for Windows 7 by Microsoft.
Based on art created by Josh Sommers, this theme consists of Optical illusions, planets of grass floating in impossible summer skies, and homages to M.C. Escher, etc as wallpapers.
The themepack contain 14 cool wallpapers and is a 6 MB download.
Head over to Microsoft to download it.
While this theme can be used only on Windows 7 Home Premium, Professional, Enterprise, or Ultimate editions, you can also always extract the wallpapers from this theme and use them. Go here to learn how to make a Windows 7 themepack.