Speedo+

This app provides most all functions a modern driver needs to avoid speeding tickets and to time/log routes. It also allows for sharing of logged routes with other Speedo+ owners.
The app supports both the build-in GPS and the DUAL XGPS150/160. The DUAL XGPS160 is a 10Hz GPS, allowing for much increased accuracy and precision resulting in a much more pleasurable experience. If you plan to use the app for performance measurements, you need the DUAL GPS.
For a comprehensive description of the app's features, please navigate to http://speedoplus.com.