Wallpaper Cycler - NuonSoft WallpaperCycler is a powerfull utility to manage all your wallpapers and to automatically cycle between your wallpapers.
John's Background Switcher - Switch backgrounds to trending imgur, reddit, tumblr threads
WLPPR - Beautiful mobile wallpapers made from satellite imagery
Variety Wallpaper Changer - Variety is a wallpaper changer for Ubuntu which is featureful, yet slim and very easy to use.
Irvue - (previously Unsplash Wallpaper) Gorgeous wallpapers on your Mac.
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!!