http://www.scangauge.com/

Looks like a neat gauge to have, plus, you can program it to indicate horsepower.
Simple to plug in and use.
Only problem I see it needs OBD II connector.

I have one. Nice little gauge. It will give you alot of info, Rpm, eng temp, tranny temp, speed, throttle position, etc. I don't know about the accuracy of the Mpg features. Overall I am very happy with it.

I have one. I use it on my LS1 conversion to read codes and make sure everything is working corrrectly etc. You can read the inlet air temp, the MAF, the throttle position etc etc.

I also used it to read and reset a bogus code on my daily driver instead of taking it to the dealer. It works well.

Don