I have a Suunto Vector HR, which is the heart rate monitor. It works great, but you have to wear the band around your chest. I don't use the HR monitor very often. I don't think I really want to know I am about to have a heart attack.
I will agree with Arrowslinger if you want something that is accurate you need the chest strap. I have and use everytime I workout a Polar with a strap that you can download you data to the computer and keep track of your workouts. I think I paid $100 for mine.
For an accurate reading you will need a chest strap. I have a GarminFR60M that is about 2 years old and still works great. It downloads the heart rate and calories used on a program that comes with the watch. There are alot more features, but I only use those. It's a normal size watch, not a huge brick like some models. I purchased it at rei. I think it is great for workouts because it motivates me to increase my pace or change my work out to keep my heart rate higher. This enables me to burn more calories. If I run for 1 hour, I'll burn around 850 calores. During my gym workouts I burn about 600.
I will second the Suunto Vector HR, however, it does have the chest strap. I have been using this watch for the last 6 month it is a very tuff watch, the HR monitoris accurate, it's watcher proof, and has a lot of other feature.
I would save your money. I don't need a heart rate monitor to tell me my heart rate is high. If I do a workout and I don't feel smoked at the end I know I cheated myself and know the next time I do that workout how much I need to push harder to get the results I want.