1)   Uranium Desktop 1.1
Uranium Desktop lets you automatically rotate your wallpapers in 2 easy steps: First you specify one or more folders where your wallpapers are located. Second, you set the time interval, ranging from every few minutes to every month.

 2)   BioniX Wallpaper 5.1
BioniX Wallpaper is a complete and advanced wallpaper changer / manager, that cycles the pictures on your desktop at your choosen time intervals.