Tseventy offers a curated collection of art-photograph wallpapers for mobile devices (it's affiliated with Poolga (previously)).
Last week, Gizmodo asked their readers to submit wallpaper-sized pictures of bugs. Today, 294 colorful images of creepy crawlies were posted to galleries on their site: 1, 2, 3, 4, 5, 6 (bandwidth alert: those pages are very picture-heavy) and also to Flickr, where high-resolution versions can be downloaded. This project is part of their weekly "Shooting Challenge". Each week's results can be seen in individual sets on their Flickr account.
30 Incredible Abstract Satellite Images of Earth "From 400 miles away, the earth transforms into abstract art. The global landscape is impressionist, cubist and pointillist." Nice NASA images from 2000, downloadable as wallpaper.
Mandolux - photographic desktop wallpapers. Just keep hittin' previous.