Speedy

-Speed meter which also keeps track of your maximum speed
-Odometer. Odometer's reading can also be saved
-Three trip meters which can be controlled independently
-Distance meter which can be used to measure the shortest distance between two given points
-Acceleration meter which measures your current and maximum acceleration
-Supports both metric and imperial systems of measurement
-Speed alarm which can be configured to go off when the speed gets too high and/or too low
-Customizable user interface. Background image, text colour and meter read out sizes can be changed.

A paid version without advertising is also available. Search for Speedy Pro from the Android market.

Known issues:
GPS still may not start at all on some devices. If you experience this, try disabling and then re-enabling GPS from your device's settings while Speedy is running.