If we're suggesting interesting sources for wallpaper, I'll add the "Art Authority" app available in the App Store. Includes about 40,000+ works of art from thousands of artists over the last several thousand years. Like having a very expensive (and huge) coffee table art book embedded on your iPad for $10. (Goes on sale from time to time.) Any of the thousands of canvases and photos can be saved as wallpaper on the iPad.