I highly recommend the Garmin 305. If that is too expensive, then I echo the previous poster. Polar is the best. My first polar HRM cost me $32.00, and while it doesn't have 5 zones, it does have the one zone I need, and I use it to this day. It was worth every penny.
I am using a polar rs200 since last april for running, biking and swimming (latter without the belt, of course), with complete satisfaction. I use it often as a regular wrist watch too. It also allows for the running speed monitoring upgrade with the footpod that can be bought separately.
Of course you will want a different model if your first discipline is running, or hiking, or fitness, etc.
btw timex watches are half the price but I never regretted spending more on the polar.