Vice City Cheat Update News
Ijust updated the Vice City Cheats link to the left as the old one had died and needed some refreshing. The New Vice City Cheats page has some cool cheats I've not seen anywhere else yet. The funniest one so far (and its unverified so use it at your own risk):
Car floats on water:
Press Right, R2, Circle, R1, L2, Square, R1, R2 during game play. A message will confirm correct code entry. Note: This code also allows helicopters to land and float on the water.

After enabling this code and are driving on the water, repeat the code to deactivate it. The car you are driving will go directly to the bottom of the water and keep going without losing any health. You will soon hit a piece of land and either end up stuck in the ground or be able to drive again. You will not lose any health during the entire time.

And one more just for the joy of killing the king of pop!
Pedestrians from Thriller:
Press Square, L1, Triangle, R2, Square, L1(2) during game play. No confirmation message will appear. Several pedestrians will resemble Michael Jackson and others will look like zombies and other characters from his Thriller music video.