I know that some of you must have done this at one time or another. Jumping on top of a fire engine and firing into the air a few times and trying to stay on for as long as possible. In GTA:SA I used this method as a way to safely take out gang members in a gang war - send the fire engine down the Ballas-filled street and jump off. You're at a safe distance to pick off the remainders. As promised, here is a diagram of CJ riding the wave.
[img_inline caption="Aww,yeah,baby."]http://i287.photobucket.com/albums/ll149/Johnny_Johnston/FiretruckSurfing.jpg[/img_inline]