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)   WallpaperWarp 1.00
WallpaperWarp 1.0 is a desktop wallpaper changer for Windows based operating systems. WW allows you to select a folder of images that you would like to be displayed as wallpaper and schedule them to change at predefined intervals.

 3)   WALLPAPER MANAGER 3.6
Just set the time of changing the wallpaper. It will automatically change the wallpaper at the fixed time. It also has the option to change the wallpaper at windows startup. There are many other options. just try it out!