Pixel Girl Presents is one of my go-to haunts for desktop images. It has thousands of desktops to choose from and all are submitted by artists who want to put their name out there and share their cherished art with others. Browse by category (like cute, anime or photographic) or by artist to get a whole bunch of expertly crafted art to complement your computer.
The gallery above is a taste of what the site has to offer, but for higher quality resolution and more selection, check Pixel Girl Presents out for yourself.
Artistic Desktop Communities
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Cutesy Pop Surrealism
3D Computer Desktops
Polished 3D-Printing Techniques
Wearable Camera Blindness Aids