Variety Wallpaper Changer - Variety is a wallpaper changer for Ubuntu which is featureful, yet slim and very easy to use.
AutoWallpaper - Using AutoWallpaper:
John's Background Switcher - Switch backgrounds to trending imgur, reddit, tumblr threads
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!!
Wallpaper Engine - Wallpaper Engine enables you to use live wallpapers on your Windows desktop.
Pixiv for Muzei 3 - Best Pixiv plugin for Muzei 3