Wallpaper Master is a highly customizable wallpaper changer and manager. It will automatically change your background wallpaper with a large range of options, and is great for indexing large collections.
You can create your own categories using images on your computer, and it will cycle through your images automatically in whatever order you specify; in a shuffle mode, listed order or based on your personal ratings. You can change the wallpaper when windows starts or every X minutes.
The program also has auto-size options to make sure your images are displayed with optimal size. Additional features include directory monitoring, global hotkeys, single click wallpaper change, automatic background color choosing, and more.