I used the signal strength of my DVB card while tuned to a certain TV channel to control the frequency being fed into an oscillator. Thus the DVB antenna can be used similar to a theremin. Actually there's nothing fancy about it, but it's in fact my first PD patch and it took me some time to make it to work. I think it's pretty nice.
Here's a video:
For more information: http://sainthuck.de/2011/02/dvbtheremin/