GTA IV is numero uno here. It's not realistic, but the cars feel like they have weight to them.
Sleeping Dogs. The feel like they move proper enough, and the feel of speed is off the charts.
Boats, Planes, Helicopters:
Just Cause 2. Without a doubt the reigning king in this department. So many options to choose from.
In terms of "racing events", Sleeping Dogs wins by a landslide. I actually enjoy racing in this game opposed to the racing events in GTA IV and Just Cause 2. It doesn't feel like a chore in Sleeping Dogs, because the routes they choose and the feel of speed makes it a well rounded experience.