Something that I use, which is fairly accurate is the SUUNTO system. You can get the optional GPS pod, which will give you speed, distance, elevation, and you can plot it on a map. The SUUNTO also has a heart rate monitor and a way to transfer everything to your computer and so you can keep workout logs. Like these:
(I know I'm slacking this month)
Plus you can add additional pods for different types of training, running, bike ect... The cool thing on the SUUNTO products is they are able to be calibrated. If you have known distance and traverse that distance with your pod on and it comes up short or long, you can go back and change it and the pod recalcualtes itself so it will be correct the next time you use it.