John's Background Switcher - Switch backgrounds to trending imgur, reddit, tumblr threads
Wallhaven - Your source for the best high quality wallpapers on the Net!
Variety Wallpaper Changer - Variety is a wallpaper changer for Ubuntu which is featureful, yet slim and very easy to use.
InterfaceLIFT - High-resolution widescreen wallpapers, desktop icons, and themes for Mac OS X, Microsoft Windows...
Wallpaper Cycler - NuonSoft WallpaperCycler is a powerfull utility to manage all your wallpapers and to automatically cycle between your wallpapers.
Simple Desktops - A collection of wallpapers designed to make your computer beautiful without distraction.