I don't have any advice of what to buy, but I do have a recommendation of what NOT to buy. I just got this one from amazon.com:
You have to place 2 fingers on the buttons above/below the display for it to register your heart rate. This is how it calculate calories, too, so you'll want to do this often during a workout. Maybe others are more coordinated than I am, but it is nearly impossible when I'm really working hard to do this - - and 90% of the time, it doesn't read my HR anyway. I am returning it (hopefully) and considering something that has a chest strap instead.
Good luck! I'll be interested in the responses, too.