I'm having a lot of fun using this "Gps Speed Sentry" app, that you can download from http://www.tchartdev.com/
This app features a series of screen showing, for the trip you're having:
- a graph on you speed
- a graph on altitude
- a compass
- some general information on actual speed, average speed, top speed, trip duration
- data on GPS satellite in sight
I find it really funny: try it if you have a gps-enabled windows mobile (or and external bluetooth gps antenna like me). The app will cost you $10, the trial version will disconnect from GPS monitoring every 10 minutes (not losing data, anyway).
Here's a screenshot, but please visit the developer's site for many other.