Well, it's not a recent mod but after hearing people talk about it at ECXC I thought I'd post something up.
Website:
http://www.scanguage.com
ScanGuage II plugs into the OBD (On board diagnostic) located just under the in cabin fuse panel.
This one little device, 4.8"W x 1.5"H x 1"D, has the ability to act as a code scanner, trip computer, and real-time gauges.
Yes, you read that correctly.
You can scan for codes, it will list them, and you can clear them.
With the trip computer function you can keep track of mileage per tank, miles to empty, hours to empty, hours per tank, average speed, average mpg, the list goes on.
Here's a small list of the real-time gauges (only 4 at a time though) that can be shown on this thing. MPG, MPH, RPM, Engine Load, Ignition timing, Water Temperature, Input Air Temperature, Throttle Body Position, Battery Voltage, and Fuel Rate.
If you buy more then one cable (which I heard Bobby did) you can move it between vehicles effortlessly.
Any other questions or if you want to see pictures just let me know.