I use this to track the ISS:
EDIT: This URL no longer works. It was a couple of maps that showed the position of the ISS. One close in and one zoomed out more. It was how I spotted the ISS as it went over the UK once. Yes - on occasion the UK does have clear skies!
What it doesn't show though is the diameter of the circle on Earth that can see it as it passes over head. For example as it passes over southern England how much of England will be able to see it?