If you want to make the most of your training, your heart rate monitors is a great starting point. Now you will need to chose the correct accessory so you can enhance the experience and achieve a more complete understanding of your performance. HRM's allow you to add more options like a Speed or Cadence sensor.  Maybe you wore your transmitter belt out or you need a bike mount for your heart rate monitor.  And if you want ot train like Lance Armstrong a Power Sensor for your polar HRM is must.