I just got a new road bike and a Garmin Edge 1000. With the Edge came a heart monitor, speed sensor and cadence sensor; but it also allows connectivity for power meters. I'm curious to find out more about them. What they are useful for and what is a good one to start with.

At my LBS, I saw a couple that were integrated into the crank. I also saw that Garmin sells some pedals for it. They both seemed pretty expensive options. Are there less expensive ones to start with?

Thanks in advance.