To be honest, with the new physics engine in GTA IV I really thought that it'd be much more difficult to pull off insane stunts in the game. I couldn't have been more wrong. The above video is by far the best stunt video I've ever seen in the GTA series.
The more incredible stunts in the video are when the guy jumps out of helicopter, seemingly about to fall to his death, only to fall into a very small pond or pool in the middle of a suburban area. Insane.