WallShuffle allows you to regularly change your wallpaper. You select a folder, then select a duration to apply a random picture as a desktop background. You can start the program in minimized mode with the "-m" argument, if you don't want to see it, or even hide the icon from the tray and forget it.
SyncWall is a basic wallpaper changer with a special feature, the ability to synchronize wallpaper changes between several workstations with a basic (and unsecured) client/server protocol. Each workstation must share the same pool of files, there is no FTP or Internet download. Other interesting features are simple multi-monitor support and the ability to add special effects to wallpaper.