It might not be cheap, but the Garmin Forerunner 405 is a powerful training device. Not only does it use GPS to track distance and log movement against time, but it can pair to accessories such as a heart-rate monitor to provide a wealth of data. The bundled software is good, and can overlay your route on Google Maps, where you can analyse your performance over differing terrain. If you've got the cash, and are interested in geeking-up your fitness regime, we can recommend the Garmin Forerunner 405.
Trusted Reviews is part of the Time Inc. (UK) Ltd Technology Network