I just installed the Scan Gauge which I received through Tone. That thing is truly awesome and it took me 15 minutes to install:

Fuel system loop status
Intake air temp
Water temp
Fuel pressure
Gallons per hour
Ignition timing
Engine loading
Miles per gallon
Miles per hour---calibrated to your tire size
Manifold pressure
RPM
Throttle position setting
Battery voltage

And best of all, reads and clears your codes should you throw one.

Now I just have to learn to pay attention to the road. An awesome gadget