Smart Wallpaper Lite is a powerful and easy-to-use wallpaper manager which makes freshening-up your desktop that much easier.
The program will automatically change your wallpaper either on each Windows startup or at specified time intervals. There's no need to touch the control panel either - everything can be administered from the system tray. The developers claim they have stripped it down so that it doesn't use up system resources like the Windows wallpaper changer although I never really noticed the latter ever did anyway.
Nevertheless, it is very lightweight, easy to use and doesn't slow down your PC while changing wallpapers. You have some limited control over how your wallpaper in changed. You can set the program to random mode or "one-by-one". Random obviously means that wallpapers are picked to appear in a random order while "one-by-one" selects them in the order of your choice. When a wallpaper has changed, the program settings automatically pop up from the taskbar which can be annoying but it disappears after a few seconds if you don't use it.
Overall, this is a simple and useful program for anyone who gets bored of their wallpaper on a regular basis.