Desktopia is a cool new application for the Mac that keeps your desktop fresh. Once installed, it automatically uploads new desktop images for you so that you're not looking at the same thing for months on end. The images are very nice and they take care of resizing them, making them work on multiple monitors, etc. You can control how often the desktop updates, you can freeze a desktop if you like it so much that you can't bear to see it go, and you can rate desktop images and their creators so that you are more likely to get desktop images that you like in the future. You can even design and submit your own desktop creations.

The only down-side is that the full version costs $20, but you can get a 10-day trial to check it out and see if it's something you like enough to spend money on.