I use a Garmin Forerunner 305. I chose it because I can also use it for hiking and skiing (you wear it on your wrist--I loop it on my handlebar). It has a heart rate monitor and optional cadence counter. I mostly use the heart rate monitor to track that I'm riding farther, faster and hillier (?!) routes with a lower heart rate. I've also confirmed my approximate max HR is 182--that's about where I was at the top of my "heartbreak" hill and wanted OFF my bike!