Variety Wallpaper Changer - Variety is a wallpaper changer for Ubuntu which is featureful, yet slim and very easy to use.
WallpapersEveryday - Gorgeous wallpapers on your desktop in just one click or auto-delivered at chosen time intervals.
John's Background Switcher - Switch backgrounds to trending imgur, reddit, tumblr threads
MuralPix Wallpaper Changer - MuralPix Wallpaper Changer and Screen Saver
Muzei - Muzei is a live wallpaper that gently refreshes your home screen each day with famous works of art.
Wallperizer - Wallperizer is a desktop wallpaper changer.