Invisible Mouse (See? It's not there.): image via infoniac.com Pranav Mistry, Pattie Maes, and Liyan Chang, researchers from MIT's Media Lab, created an invisible mouse using an infrared laser beam on the right side of a laptop keyboard and an infrared camera on the right side of a laptop screen. Their prototype cost them all of $20. Chances are the invisible mouse will cost you even less.
... That is, if the idea is picked up by computer manufacturers.
The tracking camera picks up the movements of the user's hand when in the perimeters of the laser beam range, and then projects the movements onto a display on the computer screen.
Invisible Mouse diagram: image via infoniac.com
At this writing, the camera registers movements of the hand and hand actions, such as clicking and double-clicking, but the researchers are working on teaching the computer more mouse commands. The problem is that, even though the mouse is invisible (aka not there), you still have to hold your hand and move your arm as if you were controlling a real mouse, and I think it would be more ergonomic (aka comfortable) if you really were using a mouse (aka piece of hardware).
No matter what happens to the development of the invisible mouse, this video introduction of it should go down as one of the cleverest introductions to a product ever. This was also written and produced by Pranav Mistry, Pattie Maes, and Liyan Chang from the MIT Media Lab.