Variety Wallpaper Changer - Variety is a wallpaper changer for Ubuntu which is featureful, yet slim and very easy to use.
John's Background Switcher - Switch backgrounds to trending imgur, reddit, tumblr threads
WLPPR - Beautiful mobile wallpapers made from satellite imagery
Wallpaper Cycler - NuonSoft WallpaperCycler is a powerfull utility to manage all your wallpapers and to automatically cycle between your wallpapers.
Becrux Wally - Wally is a Qt4 wallpaper changer, using multiple sources like files, folders, FTP remote folders, Flickr, Panoramio, Ipernity, Photobucket, Buzznet, Picasa, Smugmug, Google, Vladstudio and deviantART images. Now it's available in many languages!!
Muzei - Muzei is a live wallpaper that gently refreshes your home screen each day with famous works of art.