Keep an eye on your speed from the windshield
Speedometer uses GPS to mark your speed and you can view as just numbers or on a visual speedometer. There aren't too many options in here, but that's ok.
Speed can be measured in km/h, mph, m/s, knots, and even mach. The one option that I totally love is the HUD mode which reverses the screen so you can set your Z10 on the dash of your car, then view your speed on the windshield. Speedometer for BlackBerry 10 is free but a paid upgrade gets you full screen viewing and kills the ads.