OK - its not a cheap option, but I finally treated myself to a Garmin Forerunner - 405.
I've used the Nike+ Sport linked up to my ipod for the last 12 months. It was great but I didnt find it very accurate but brilliant value if you already have a Nano Ipod. (£25).
Anyway - I decided I needed a treat.
I love my Garmin 405. I cant tell you how brilliant it is - its really easy to keep a training log (something I have been hit and miss). There isnt any faffing around before you get out of the door. And because its GPS its as accurate as you are going to get.
You can compare past runs and do loads more.
I am by no means fast but I am hooked on running/plodding.