http://leapmotion.com/ this is being released later this year. Preorders are being taken now. $69.99
I saw that on the Verge, the only thing that worries me is that it seems like a cool demo. That's it. In order for something like that to be successful developers need to implement it. Having it built into the iMac would allow Apple to control it at the system level. I would love to see an Apple TV controlled by swiping and hand gestures, this is much more intuitive to me than talking to Siri.