Every now and again, someone thinks outside the box, and creates something magnificent - in this case, Jean Noël Lefebvre has created a 3D touch-less gesture sensor, in the form of an Arduino shield. It doesn't use infrared or ultrasonic sensors, but capacitance. The sensor can detect position and distance of your hand, allowing many gestures, such as swipe, rotate and push, allowing small scale Minority Report style computer gestures.
This is a great example of next-level control. Adding the 3rd dimension allows greater control of parameters, and could be used in musical applications, similar to the Alesis AirFX, or as a game controller, allowing multiple actions to be performed with one hand using gestures.
The 3D pad is still in an early prototype stage, but you can see it in action in the video below. It's basically a collection of CMOS chips, and an Arduino board, making it an inexpensive and robust project.
We will hopefully see this integrated into projects in the future; touch-less control (especially 3-dimensional) is such a good idea. You can read more, and keep up to date at the project website. You can help contribute to the success of this project, by voting for it on the Atmel AVR Design Contest at http://goo.gl/aU4ThQ.