Unlock All Weapons:
At the main menu, press R1, L2, Square, Circle, R1, R2, L2.
Unlimited Ammo (wont work in undercover mode):
At the main menu, press R1, R2, R1, R2, Square, Circle, Square.
Invincibility (wont work in undercover mode):
At the main menu, press Square, Square, L1, R1, L2, R2, R2.
Immunity (wont work in undercover mode):
At the main menu, press Circle, Circle, L1, L2, R1, R2, Square.
Unlock all Missions:
At the main menu, press L1, R1, L1, L2, Square, Square, Circle.
Unlock all Vehicles:
At the main menu, press L1, L1, Square, Circle, L1, R1, Circle.
For the most fun of this cheat, at least have invincibility, all weapons, and unlimited ammo all on. Go to Coconut Grove in Miami and where it shows the straight road crossing there will be a building. Go in it with a car or by human and blow the mall up.(By shooting stuff)!!
(supplied by: CheatBoy)
Go to Miami. Go to the Miami Beach start point. Make the first left and keep going until the end of the road and make a left. Keep going (looking left) until you get to the alley with the stairs(it is near the next road). On the right there will be a set of stairs. Start walking up them. When you are almost to the top, start running to your left and press x. You will get launched off the steps. This is a good way to dodge bullets from cops when you are being shot at. You will also not lose any health.
(supplied by: porlia)
The disappearing felony bar!:
When you're "full on felon" go in you're house (any one) and you're bar will disappear!
(supplied by: Joe Dirt)
Secret Miami Car:
From your starting at your house in Miami travel left out onto the main road to the first road/ Bridge that you come to on the left then go to the first road on the left travel all the way down to the end where there is a garage, the car is in the garage during Free Ride.
(supplied by: jststiehl)