Power meters

Best thing to do is read the book about them to learn all you ever wanted to know.

Check this out

I have the top of the line wired PM from Power Tap that comes with training wheel. List price is $999 and I got it with a 20% off coupon from Performance with 10% future rebate so I paid $720...great tool if you know how to use it or have a coach. They also have wireless version now that is more expensive.

I also have Zipp 404s with power tap hub I use for racing.

Other brands of real power meters are more expensive initially.

This offers a pretty nice review as well:

http://www.biketechreview.com/archive/pm_review.htm

I have a powertap and love it. That seems to be the "best bang for your buck." Seriously, your training will appreciate it, but it will also revolutionize trainer riding. Soon, you'll find you enjoy the trainer more than outside. Okay, well nothing really compares to being in the great outdoors, but it's so much easier to execute your training sessions on a trainer than outside, especially when you're getting feedback every second .

A related question:  I have a Kinetic Road Machine and see that they also sell a power meter for $50.  Is there a reason to get one of the more $$ power meter setups instead of using this cheaper alternative?  Is it a matter of accuracy/precision/repeatability?