Deskland is a series of "adaptive wallpapers" that respond to the placement of your desktop icons. Pick the Sky theme, drop some icons and clouds appear underneath. Pick the Forest theme, drop some icons and the trees clear out to make way. The site says there are 13 themes at the moment but I see no list of them... so if you're a Windows user, go snag it and see what they are! It's a simple idea but a delightfully whimsical one.