If you're bored of that useless, still image for your desktop wallpaper, Live Desktop is a Mac app that gives you a selection of animated themes to choose from.
Once the app's loaded up, you can choose from a variety of desktops, all of which you can see in action in the video above. Stylistically they're not going to appeal to everyone, and sadly, you can't add in your own videos now. Still, if you like the idea of moving pictures as a desktop, Live Desktop certainly does the trick provided you're a fan of their themes. If not, you can always make your own with an animated GIF or video.