there are other brands that r cheaper but i like my scanguage 2, plus u can change the color to match ur interior lights. ScanGaugeII - Scan Tool + Digital Gauges + Trip Computers ScanGauge II at TheGadgetHome
I have one and love it. Used it in my 08' Tacoma before I sold it, now resides in my 4Runner. It's nice if you have larger diameter tires, while your driving you can adjust the mph and match it to a GPS. Then it will give you a better estimation of mpg and miles left on the tank and etc vs the 4Runner's on board computer.
It also stores your current data along with tank data. I love to check the max RPM, max speed, MPG, gasoline used, etc.