Yesterday I found out that Transport for London lifted all restrictions for commercial use of its data that it has made available for developers.
It basically shows a map of London and then shows all the spots where traffic cameras are installed so that you can click on them. The data is updated every 3 hours I think but I haven't checked that claim yet. Use this if you're a London commuter and want to check the traffic before you hit the road.
Oh, and this app uses the geo location stuff so that I know where to zoom in first. But if you're not based in London it zooms in over Trafalgar square by default.