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
Muzei - Muzei is a live wallpaper that gently refreshes your home screen each day with famous works of art.
Wallpaper Engine - Wallpaper Engine enables you to use live wallpapers on your Windows desktop.
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!!