I remember a while back we were discussing if someone have put out an aftermarket MPG gauge and some one found a place in finland that sells one. Well here is one that is sol in the US. It is not the prettiest gauge in the world - but it has a lot of useful data to show (like MPG, voltage, coolant temp, throttle position etc).
At 129 bucks you cannot expect it to look that beautiful. I will get one as soon as I have the money for it.
http://www.scangauge.com/