Adrenaline Pill
Rescue 100 patients in paramedic missions and go to your hideout.
(Thanks to chitownzfinest_31@yahoo.com)

All Weapons
Press R2, R2, L1, R2, Left, Down, Right, Up, Left, Down, Right, Up during gameplay.
(Thanks to DWALFYBOY)

Armor
Press R2, R2, L1, L2, Left, Down, Right, Up, Left, Down, Right, Up during gameplay.
(Thanks to chitownzfinest_31@yahoo.com)

Better Handling
Press R1, L1, R2, L1, Left, R1, R1, Triangle during gameplay.
(Thanks to chitownzfinest_31@yahoo.com)

Blow Up All Cars
Press L2, R2, L1, R1, L2, R2, Triangle, Square, Circle, Triangle, L2, L1 during gameplay.
(Thanks to chitownzfinest_31@yahoo.com)

Borgnine Taxi
Deliver 100 taxi passengers and go to the parking lot of HEAD Radio in Harwood.
(Thanks to chitownzfinest_31@yahoo.com)

Faster Gameplay
Press Triangle, Up, Right, Down, Square, L1, L2 during gameplay.
(Thanks to chitownzfinest_31@yahoo.com)

Faster Time
Press Circle, Circle, Circle, Square, Square, Square, Square, Square, L1, Triangle, Circle, Triangle during gameplay. Repeat as desired.
(Thanks to chitownzfinest_31@yahoo.com)

Flamethrowers
Extinguish about 20 fires in each of the three areas and go to your hide-out.
(Thanks to chitownzfinest_31@yahoo.com)

Flying Cars
Press Right, R2, Circle, R1, L2, Down, L1, R1 during gameplay. Press Up while driving to fly.
(Thanks to chitownzfinest_31@yahoo.com)

Fog
Press L1, L2, R1, R2, R2, R1, L2, X during gameplay.
(Thanks to MR X)

Full Armour
Press R2, R2, L1, L2, Left, Down, Right, Up, Left, Down, Right, Up during gameplay.
(Thanks to MR X)

Full Health
Press R2, R2, L1, R1, Left, Down, Right, Up, Left, Down, Right, Up during gameplay.
(Thanks to MR X)

Gorier Gameplay
Press Square, L1, Circle, Down, L1, R1, Triangle, Right, L1, X during gameplay. Some weapons will blow off body parts and increase bloodiness. (Note: a message saying it is correct will not appear).
(Thanks to chitownzfinest_31@yahoo.com)

Health +20
Hijack an ambulance.
(Thanks to chitownzfinest_31@yahoo.com)

Hidden Package Bonuses
Bonuses will be located in your safe house.
10 Packages: Pistol
20 Packages: Uzi<
30 Packages: Grenades
40 Packages: Shotgun
50 Packages: Armor
60 Packages: Molotov Cocktail
70 Packages: AK47
80 Packages: Sniper Rifle<
90 Packages: M16/Flamethrower
100 Packages: Rocket Launcher
(Thanks to chitownzfinest_31@yahoo.com)

Improve Handling
Press R1, L1, R2, L1, Left, R1, R1, Triangle during gameplay. Press the Left analogue stick to jump.
(Thanks to MR X)

Infinite Ammo
Keep doing the All Weapons code until get the selected weapon to 9999 shots.
(Thanks to chitownzfinest_31@yahoo.com)

Infinite Health Icons
Rescue 50 patients in paramedic missions and go to your hide-out.
(Thanks to chitownzfinest_31@yahoo.com)

Instant Health
Press R2, R2, L1, R1, Left, Down, Right, Up, Left, Down, Right, Up during gameplay. Also heals your vehicle (it will still look damaged though) and extinguishes fires (do it quickly).
(Thanks to chitownzfinest_31@yahoo.com)

Invincibility
Press Left, Right, Down, Up, Triangle, Circle, Triangle, Up, Down, Right, Left during gameplay.
(Thanks to chitownzfinest_31@yahoo.com)

Invisible Cars
Press L1, L1, Square, R2, Triangle, L1, Triangle during gameplay.
(Thanks to chitownzfinest_31@yahoo.com)

Jumping Cars
Enable the Better Handling code and press L3 or R3 to jump.
(Thanks to chitownzfinest_31@yahoo.com)

Lower Wanted Level
Press R2, R2, L1, R2, L1, Up, Down, Up, Down, Up, Down during gameplay.
(Thanks to MR X)

Max Health 125
Get a nice car, find a hooker, pick her up, drive to a secluded spot, and watch the car rock until you hit 125 (you might need to do it more than once if your health is really low). Lasts until you die.
(Thanks to chitownzfinest_31@yahoo.com)

Money
Press R2, R2, L1, L1, Left, Down, Right, Up, Left, Down, Right, Up during gameplay.
(Thanks to chitownzfinest_31@yahoo.com)

Normal Weather
Press L1, L2, R1, R2, R2, R1, L2, Triangle during gameplay.
(Thanks to MR X)

No Wanted Level
Press R2, R2, L1, R2, Up, Down, Up, Down, Up, Down during gameplay.
(Thanks to chitownzfinest_31@yahoo.com)

Overcast
Press L1, L2, R1, R2, R2, R1, L2, Square during gameplay.
(Thanks to MR X)

Pedestrian Fight
Press Right, R2, Circle, R1, L2, Down, L1, R1 during gameplay.
(Thanks to MR X)

Pedestrians Riot
Press Up, Down, Left, Up, X, R1, R2, L2, L1 during gameplay.
(Thanks to MR X)

Pedestrians With Weapons
Press R2, R1, Triangle, X, L2, L1, Up, Down during gameplay.
(Thanks to chitownzfinest_31@yahoo.com)

Play As Pedestrians
Press Right, Down, Left, Up, L1, L2, Up, Left, Down, Right during gameplay. Can be done multiple times (hundreds actually) to change to different characters.
(Thanks to chitownzfinest_31@yahoo.com)

Police Bribe Powerups
Kill about 40 criminals in each of the three areas and go to your hide-out.
(Thanks to chitownzfinest_31@yahoo.com)

Programmer's Message
When you are fighting the guys with bombs strapped to their chests, try to get over the walls there and you will see a programmer's message.
(Thanks to EminemJak@aol.com)

Rain
Press L1, L2, R1, R2, R2, R1, L2, Circle during gameplay.
(Thanks to MR X)

Raise Wanted Level
Press R2, R2, LI, R2, Left, Right, Left, Right, Left during gameplay.
(Thanks to MR X)

Recover From Tipping Over
Enable the Better Handling code and when you flip over, if your car is not on its roof, press Square+X.
(Thanks to chitownzfinest_31@yahoo.com)

Rhino (Tank)
Press Circle, Circle, Circle, Circle, Circle, Circle, R1, L2, L1, Triangle, Circle, Triangle during gameplay.
(Thanks to chitownzfinest_31@yahoo.com)

Rioting Pedestrians
Press Down, Up, Left, Up, X, R1, R2, L2, L1 during gameplay.
(Thanks to chitownzfinest_31@yahoo.com)

Run Longer
Don't hold the X button. Press it repeatedly. If you do it right, you should be able to run for a long time.
(Thanks to chitownzfinest_31@yahoo.com)

Skip Kenji Missions
Do a mission for Kenji, then go work for Ray, and eventually, work for Donald Love, who will have you kill Kenji.
(Thanks to chitownzfinest_31@yahoo.com)

Slower Gameplay
Press Triangle, Up, Right, Down, Square, R1, R2 during gameplay.
(Thanks to chitownzfinest_31@yahoo.com)

Tank
Press Circle, X, X, X, X, X, X, R1, L2, L1, Triangle, Circle, Triangle during gameplay.
(Thanks to MR X)

Violent Pedestrians
Press Down, Up, Left, Up, X, R1, R2, L1, L2 during gameplay.
(Thanks to chitownzfinest_31@yahoo.com)