ArtPlus ePix wallpaper calendar - ArtPlus ePix wallpaper calendar is FREE software!
National Geographic for Muzei - National Geographic pictures for Muzei
Variety Wallpaper Changer - Variety is a wallpaper changer for Ubuntu which is featureful, yet slim and very easy to use.
AutoWallpaper - Using AutoWallpaper:
Wikimedia Commons for Muzei - Muzei plugin that displays the Wikimedia Commons picture of the day
Wallpaper Engine - Wallpaper Engine enables you to use live wallpapers on your Windows desktop.