Collision Detection
My collision detection with the environment is near-perfect. The player doesn't (usually) get stuck in the geometry, and the bounce effect works well.
The collision with other cars, though... not so much. It just makes a bounding sphere that's a bit too big. The cars don't respond as well while they're in motion. It looks kinda tacky. But it works, and if I decrease the amount of cops so the player's not swamped with them it won't be so bad.
Also, I made a chase camera, because it took me all of 10 minutes to do so. :)