Simple speedometer app and widget for Android 2.2+ (and some 2.1 with different problems - use at your on risk ;-))
(screenshots in German but app in English)

Tip: on small screens hide timer or compass in settings
FAQ's: http://www.x-droid.de

Android-Speedometer is certified as a safe app by http://www.appoozle.com

numeric values for:
- speed (km/h, mph or kn)
- altitude (from GPS or webservice)
- cyclometer (km, mi, nm)
- timer
- digital clock
- compass
- max. speed
- average speed

- route recording and speed trend diagram
- accelerometer with variable start and stop speed
- time to distance (eg quarter mile)
- stopwatch
- location (link to map available)
- available satellites and accuracy
- anchor alarm (leaving radius alarm)
- Headup-Display (HUD = MIRRORED view)
- automatic night mode
- custom font colors for day and night mode
- landscape view
- widget for homescreens (Widgets do not work properly if app is installed on SD card. If you want to use the widget you must install the app in the internal memory of your device, if not App2SD is full supported.)
- save location and start pedestrian navigation to it (find your car)
- gpx, kml and csv file export and send for data exchange (e.g. with google earth)
- spoken speed warnings (any number of adjustable speeds) or spoken speed (NEEDS to install Text-to-Speech!!!)

Developer tested on
Android 4.0.3: HTC Sensation (with Revolution HD 6.1.0)
Android 3.2: Samsung Galaxy Tab 10.1, HTC Flyer
Android 3.1: Samsung Galaxy Tab 10.1
Android 2.3: HTC Sensation, HTC Incredible S, HTC Flyer, Motorola Defy (with Cyanogen 7.1), Samsung Galaxy Ace
Android 2.2: HTC Desire, HTC Desire HD, Samsung Galaxy S, Samsung Galaxy S2, Samsung Galaxy Tab, Motorola Defy
Android 2.1: Motorola Defy (sound crash on anchor alarm, map crash and temporarily problems with speed update)

If anyone wants help translating the app to other languages - please send me a mail. It's very easy!
Please mail problems and suggestions! I will try to help in every case.

Screenshots: