Use a regular Bicycle Computer to keep track of your speed and distance covered, and if a regular cyclometer does not provide quite enough detail for you, try one of the Garmin Edge Bicycle GPS Systems.

Computers and GPS Systems
Blackburn Atom 4.0 Cycling Computer Only $39.95		Garmin Edge 500 GPS Bike Computer Basic Version Only $249.95
Garmin Edge 500 Bundle GPS Bike Computer With Heart Rate Monitor and Cadence Sensor Only $349.95		Garmin Edge 500 Team GPS Bike Computer With PremiumHeart Rate Monitor and Cadence Sensor Only $369.99
Garmin Edge 800 GPS Bike Computer Touchscreen - Basic Version Only $449.95		Garmin Edge 800 Bundle GPS Bike Computer Touchscreen with Hear Rate Monitor Cadence Sensor and Navigation Only $649.95