Two more apps
Resurrecting an old thread here..
I found a few vehicle-specific clinometers on accident just now.. I purchased a couple of the nicer looking ones:
The black and green one is named "Vehicle Clinometer / Tilt meter" and the gray and red one is named "LandMeter." The former is $1.99 and I think the former has some of the cooler features (GPS, customizable warnings + alarms, compass). The latter is $0.99 and looks nicer (except for the Geo Tracker

); it basically just shows the angles and has customizable alarms.