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!!
Variety Wallpaper Changer - Variety is a wallpaper changer for Ubuntu which is featureful, yet slim and very easy to use.
Pixiv for Muzei 3 - Best Pixiv plugin for Muzei 3
Wallpaper Cycler - NuonSoft WallpaperCycler is a powerfull utility to manage all your wallpapers and to automatically cycle between your wallpapers.