Sygic makes some very popular navigation apps, and now the company is branching out a bit with a free app called Speedometer. It uses your iOS device's GPS receiver to provide your current speed and trip mileage, as well as warn you of fixed speed and red-light camera locations. The app also provides a way to warn other drivers of police radar, traffic incidents and other dangers.
I tried Speedometer on a short commute this morning and the app immediately listed the closest known speed cameras, although none were on my route. I also set a maximum speed so the app would warn me if I was going too fast.