Wallpaper Master allows you to change your desktop wallpaper automatically every X minutes

Wallpaper Master is a highly customizable and easy to use wallpaper changer and manager. It will automatically change your background wallpaper with a large range of options, and is great for indexing large collections. If you're the kind of person that changes their wallpaper frequently then you'll love this program. You can have this utility change your wallpaper at whatever interval you specify. It has a lot of features and it's completely free!