SpaceNavigator huge price drop
3Dconnexion makes a spiffy 3D USB input knob that looks like the Griffin i-Mate, but does much more. It has 6 degrees of motion: twist L/R, roll (tilt) L/R, roll (tilt) F/B, push L/R, push F/B, push U/D. Previously $250, the new version has been lowered to $59. Yowza!
It could be used like an i-drive knob for your CarPC front ends. For example, twist for volume control, tilt to navigate menus and lists, push L/R for switching functions, etc. It also has two programmable buttons.
Windoze only at this point. Linux support seems likely based on previous products, but no indication of Mac OS suport.