Do you use a cyclocomputer, is it wireless and what does it tell you? I'd like one that will tell me power output, but that needs a measure of torque - how does that work? I'm also interested in measuring cadence, speed and distance travelled.

Answer from a beginner - measuring torque is going to be expensive. Big time.

I use a Cateye with wire that gives cadence, speed, ET, distance, and average speed. Cost about $40.00. I felt that having a wire dangling around that saved $100.00 was a status symbol in itself. Cateye instructions and quality are way better than the dept store breeds, by the way. The clock was a bit tricky to set, but otherwise straightforward. Be sure to calibrate your meter to your tire.

Start with a decent $100 unit before you go to a $1000 model with it's own wheel.

You can take a look here for reviews of various power meters. The article is a bit dated, but it should provide a good starting point. As for the other functions, you'll likely need a more traditional cyclocomputer in addition to the power meter. I personally use a CatEye Astrale 8 (probably the same model as Nermal's), which, as he mentioned, measures cadence in addition to the usual speed, time, distance, ... One nice thing about the CatEye is that it measures speed from the rear wheel instead of the front, so that you only have to route one wire down past the bottom bracket instead of a second wire down the fork to the front wheel.