I want to recommend the "Scangauge II", a small add on device which displays various stats about your car, most importantly, mpg. It connects to the OBD2 port on all cars made after 1996. The real-time display of mpg is incredibly useful and it makes efficient driving into a fun game. It costs $160, but it's well worth it.
I used to drive like most young men and I thought pretending to be a race car driver was the only way to enjoy the driving experience. Now, I strive for the most fuel efficient way to get from A to B. I would guess that using the SG2 has given me an extra 5 mpg, and I've only had it 2 weeks, and my wife does most of the driving (I ride a bike to work).
http://www.scangauge.com/
PS: I don't work for them
wize1 
Threaded Mode
