Wallcat - Enjoy a new, beautiful wallpaper, every day.
Wallhaven - Your source for the best high quality wallpapers on the Net!
Splashify - Beautiful desktop wallpapers for Mac and Windows
InterfaceLIFT - High-resolution widescreen wallpapers, desktop icons, and themes for Mac OS X, Microsoft Windows...
Irvue - (previously Unsplash Wallpaper) Gorgeous wallpapers on your Mac.
Simple Desktops - A collection of wallpapers designed to make your computer beautiful without distraction.