If you are interested in recording your power output while training or racing then you might want to consider Ergomo. They are a German-based company that has been around for eight years. BiciRace.com had a look at their goodies while roaming the floors of EICMA.
Their power output system uses the bottom bracket to measure watts. We had a good look at the system cutaway model while in Milano. Inside the bottom bracket the power output is measured by two optical sensors. The main difference here is that this is a non-contact sensor, so there are no components to be mounted on moving parts. It presents a whole different theory on looking at power measurement, as opposed to using the cranks or a rear hub.
Up top there is nice control unit, which has been completely redone for the new season. The control is finished with a soft rubber that feels nice under the fingers (note, the control unit in the picture is the previous version without the soft rubber finish.) The unit provides all of the normal features of a cycle computer, including speed, distance, etc. In addition is altitude, heart rate and of course, your watts. The read-out is clear and large, great for when you are doubled-over in pain from too many intervals.
See Ergomo's website for more information.