CamSam - Radar Detector is an app that turns your mobile phone into a highway radar detector that lets you know ahead of time if there's a speed camera coming up so you won't be caught by surprise, which could be expensive if you're going faster than normal (which you really shouldn't be doing, by the way).

The app comes with a database of over 47,000 radar traps and it will let you know when you come near one of them. Plus, it updates frequently so that new speed traps never catch you by surprise.