Desktoptopia automatically updates your monitor with fresh designer desktops
A free desktop wallpaper manager, weighs less than a mega byte, delivers fresh wallpapers which includes broad range of designs eg. 3d, illustrations, nature, art etc.
Its available for both Mac and PC, though still beta, give it a shot, and I hope you will enjoy it as much as I do. :)
Here is a link: http://www.desktoptopia.com/