I like Trapster. Its a “crowd-sourced” speed trap reporting system. Its integrated with Google Maps so it also includes the Google Maps’ traffic flow information. The quality of the speed trap information relies on user participation, so it works better in more populated areas. You should also have a good mobile mount for your device if you plan to report traps so you can tap the right buttons without too much distraction. Fortunately, in my car I can tap the screen without taking either hand off of the steering wheel.
I also like Global Real Time Traffic & Radar. Its also a crowd sourced information application.