A few weeks ago Camron and I invested in Polar FT7 heart rate monitors. Mine (purple) cost me $70.00 at Best Buy. I think the men's one (silver and black) is about $10.00 more.
These heart rate monitors are great for keeping track of the calories you burn during a workout and also knowing your heart rate. I use mine to measure the calories I burn so I know how many extra calories I need to eat that day. You can transfer your training stats to your profile on polarpersonaltraining.com. This helps keep track of all your workouts. You can change the watch battery yourself, which is great! You don't have to bring it in anywhere.
These watches are pretty affordable and seem to be one of the most popular brand and model within this price range. You can of course purchase something fancier with more capabilities. For a simple, easy to use and good quality heart rate moitor these do the trick. You can find cheaper ones at Wal-mart, but I think you might as well invest a little extra for better and longer lasting quality.
I have read Reviews on the FT4 model in which the heart rate monitor would conflict with other machines in the gym or other heart rate monitors. In other words the user could not get a reliable reading of their heart rate. I have not found this to be a problem with the FT7 model. Camron and I have used them at the same time while working out together and have found no problems with our readings.