It'd be neat to have a mod that replaces the vehicle cameras with a custom one for both third and first person. Reacts to forces and rotation and stuff, in third person it's like a chase cam in a racing game. In first person, can "simulate" g-forces or something. Preferably would auto-center when the mouse stops moving after a configurable amount of seconds.
The main thing is the third person aspect of it, to make driving more fun. Would probably be a client mod.
Also, I was looking for a client mod that let you freeze the camera in place that I used to use, while you can still control your blockhead normally, but I can't find it anymore.