Mac OS X only: Using your Mac's iSight camera to detect the hand gestures you make in front of it, free utility FluidTunes controls your iTunes library playback based on those motions. File this under "really cool but not sure I'd actually use it every day": you swipe your hand back and forth in the air in front of your Mac to move through your iTunes library in Cover Flow mode, and then swipe at a button to play a selected album. FluidTunes shows what you look like on your camera behind your album covers, so you can centre your hand over buttons to press them. (It's dim, but it's there—in the screenshot above the user's hand is at the bottom of the screen.) While not touching the keyboard, mouse, or any other digital remote to play your music is amazing, you'll look like a flailing crazy person while you use FluidTunes. Here's a video demo.
FluidTunes is a free download for Mac only.