Took a 'break' from working on my game to make a hover car.
Took me forever to add a basic self righting / stabilisation mechanism due to the confusing nature of rotations, gimbal lock and quaternions
Uses a configurable grid of hover forces under the car also so it isn't disturbed by small objects
Can set stabilisation force for when on ground separate from when in air
If you set the stabilisation force high for on ground it will stay level even when climbing a slope
And just played with it using the wireless xbox controller, tis fun!
Used Tattiebogle on Mac to use the controller
Link: tattiebogle.net --- Xbox360Controller