Ren,
Most folks will point you to
Polar. They are the reknowned
leaders in this field. Lots of models and exposure. But, I won't.
After a year when the battery in the chest strap dies, you have to send it
back to Polar for a new one. Every model. Real convenient... :jerkit:
That said, look at the offerings from
CardioSport. Replaceable chest strap batteries and a MUCH better price point. That's what I use.
Coop
We've carried Polar HRMs for years at my bike shop, as well as others on and off. The Polar's have been by far the most reliable and user friendly. As several have said, they are the leaders in the category. It is a deserved reputation.
The chest strap batteries are rated to 10,000 hours of use. That's two hours a day, five days a week, for two years.
A WearLink 31 chest strap with a changeable battery goes for $50 or so.
If you're on a budget, I'd look at the F6. It has most of the features that most people want, including a coded transmitter, for $120.
If you want to go all out, the S725X is a sweet one. It's got all the heart rate features you could want, as well as all the features you'll find in a cycling computer (speed, distance, cadence, etc.). It comes with the WearLink chest strap. It costs $360, so it's not cheap, but if you want one unit to keep track of all your workout info, plot HR vs. speed vs. workout time vs. cadence vs. whatever on your computer, it's the way to go.
There are also a bunch of others, but those are probably the two that we sell the most of. That doesn't mean that they are the best ones for you, but it's a good couple of HRMs to start looking at.
As an aside, if anyone needs any info on cycling related stuff, I'm more than happy to help.