A while ago I was trawling the internet to try and figure out if I was getting the best deal on my mobile, and came across a site called Bill Monitor
I was a bit dubious at first, but having used the site for a while I am quite impressed with it. You tell it a bit of information about your contract and it lets you know when you can save on your current contract and how to make the best of what you currently have.
A rough calculation suggests that if every resident in County Durham used this service and acted on the suggestions, we would collectively save £30m a year!!