Thanks for all the replies - I do accept that a fully waterproof jacket isn't going to be helpful when sweating, but my current jacket offers no protection and was stuck to my skin making me colder within minutes of the torrential downpour I was running in.
The windstopper gilet seems to be a good recommendation - cheers to all who answered!
I've run with both a Nike+ and RunKeeper (iPhone GPS running app). Have to say if I'm running alone the two match up pretty well, if I'm running with my partner, who has a slower pace, then I usually see the Nike+ distance go up as I end up doing a lot of running on the spot! They are measuring different things and the Nike+ accelerometer has a known +/- 5% accuracy based upon the motion of your feet, whereas GPS is only accurate to approximately 12 feet. GPS also has the problem of not working if a direct line of sight to the satellites isn't available such as heavily built up or wooded areas.