Thanks to a new, totally free Kinect project called Synapse, you can turn your body into an instrument.
It's an open-source application for Windows and Mac that allows you to control music and visual elements in Ableton Live, Quartz Composer and other programs using Kinect. Above is a demonstration from its programmer, Ryan Challinor, who works at Harmonix when he isn't making cool stuff like this.
In his own words, Synapse for Kinect "allows you to do things like play with a dubstep theremin while you have fire shooting out of your hands." Finally, my dreams are starting to come true! Follow that first link for the download and documentation.