Quite a few company's make power meter's for bikes. They usually have a various array of strain gauges and other measurement devices in the cranks. It is essentially a dyno for your legs...
The most well known being a company called SRM, I'll try and dig up the data sheet from one of his standing start sprints where it gave values for watt's and Nm of torque that he put into the cranks.

*EDIT* for those interested, the technology is pretty cool.
http://www.srm.de/index.php/gb/technology/function