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!!
AutoWallpaper - Using AutoWallpaper:
Artpip - Artistic wallpaper for your desktop, refreshed daily.
Pixiv for Muzei 3 - Best Pixiv plugin for Muzei 3
Kuvva - Kuvva is the source for beautiful wallpapers.
John's Background Switcher - Switch backgrounds to trending imgur, reddit, tumblr threads