The basic $50 Polar heart rate monitor is pretty good. Not many bells and whistles, just shows you your heart rate on a wristband from a strap around the chest. I think it can also track your minimum and maximum for the session. Also compatible with most gym treadmill heart rate displays as well. I don't actually use it much anymore because having a chest strap on is kind of uncomfortable. I use speed and duration on the treadmill instead.