www.hrm-reviews.com displays a good range of heart rate monitors all broken down in to activities or brands. All link to Amazon where you can buy with your own account.
The Garmin Forerunners have built in GPS which really helps as you can also see how far you have run not just how fast.
Some of the Polar and Suunto watches can be used with a foot pod to record distance, but they are usually an extra. You could go for one of these as a cheaper option and upgrade later, if you feel you want to know distance as well.