Exercising while using a heart rate monitor can give you important health information.
There are several heart rate monitors at Bike Nashbar.
Of the non-cyclocomputer ones, Suuntu is the only one with download feature
Suunto T6 Fitness Computer $249.95
This Sigma looks adequate for my needs
Sigma Sport PC14 Heart Rate Monitor $39.99
I don't know what quality this is
Amazon has a wider selection including an intriguing GPS + chronograph + Hr monitor made by Garmin
Garmin Forerunner 305 GPS Receiver With Heart Rate Monitor $175.29
Polar is the industry leader, so far as I can tell. This basic HRM looks like it would meet my needs
Polar FS2 Heart Rate Monitor Watch