At Maker's Faire 2007, Trossen Robotics had some cool toys at their booth. One system was the Magic Air Tubes. They have a video along with a list of the hardware they used for the project.
Trossen Robotics used IR sensors to detect how far your hand was from the sensor. From there, that value was translated into how much power would be sent to the fan at the bottom of the tube. The closer your hand was, the further up the ball in the tube went.
Now only if I can hook that up to the Internet, I'd be set. The Internet is just a series of tubes, right?