Check out http://torque-bhp.com/ for Android.
I use it and think it is great.
the stuff I find useful:
Oil, Air, Intake and Gear temperatures
GPS and Sensor speed
Air to fuel ratio
Average Ltrs per 100 KM
And I might find the 0-100 and 1/4 mile stuff fun if it didn't involve breaking the law but take the results with a grain of salt.
It also has the ability to upload to a server where you can see sensor readings on google maps.