Want to tell about an app I built. It was previously called uHud but has now been renamed to the more explicit "Speedometer HUD".
Shows your speed in mph or km/h. There's also Google Maps integration allows you to view your location on the map while viewing speed. I can also act in HUD mode and you can put it on the dashboard of the car and see the speed or map on the windshield.
Future releases will include, inter alia, a compass and the ability to choose a "home position" as one can always see the distance to.
App cost approximately $1.