A couple of years ago I bought a running watch. The Garmin Forerunner 305 (http://bit.ly/NQzt0). At the time I bought it, I had the old 201, so it was really a step up. Newer models have come since, but this one does the trick – if you remember to charge it; today it died on me around 15K.
Apart from the GPS and the wireless heart rate monitor, it tell you all you need to know when sweating it out on the road. As an added benefit, you can upload your training session to Garmin Connect (formerly known as MotionBased). I know, you can live without it, but personally I really like to keep track of your training sessions and see how you did compared to e.g. last year at the same time.
A few words about the training: this and also next week I still work on getting some miles into those old legs. After this I will go for speed for a few weeks doing intervals and after this revert back to the training program derived by Lars Bom (to the Danes: yes the actor). Drop me a line if you are interested.
Happy running to all.