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 Delphi 4.0 Cycling Computer Only $49.99		Garmin Edge 205 GPS Unit for Bicycles $249.99
Garmin Edge 305 GPS Bike System with Heart Rate Monitor $349.99		Garmin Edge 305 GPS Bike System with Cadence Sensor $349.99
Garmin Edge 305 GPS Bike Bundle GPS Unit, Heart Monitor & Cadence Sensor $399.99