Rockstar
I'm not sure if sitting at a computer is an activity that warrants monitoring your pulse rate. However, if you have heart problems and would like to keep your heart beat in check (maybe those NSFW are not such a good idea when your rate is high), then Asus has a laser mouse that will do just that.

In addition to the integrated pulse rate sensor, the Asus Vit W1 Wireless Laser mouse features 1,200 dpi resolution, a 2.4GHz USB receiver, 30-foot wireless range, and five programmable buttons.