At the main menu (the livingroom), go to the options screen and then enter the codes.
A horn will confirm correct code entry.
Invincibility:
Hold down L1 + R1, then press Triangle, X, Triangle, X
Different Camera: Hold down L1 + R1, then press Circle, Circle, Circle, X
Fast Cars: Hold down L1 + R1, and then press Square, Square, Square, Square
Faster Cars: Hold down L1 + R1, then press Triangle, Triangle, Triangle, Triangle
Grid View: Hold down L1 + R1, then press Circle, X, Circle, Triangle
Horn Button Jumps: Hold down L1 + R1, then press Square, Square, Square, Triangle
View Credits: Hold down L1 + R1, then press X, Square, Square, Triangle
Show Speedometer: Hold down L1 + R1, then press Triangle, Triangle, Circle, Square
Trippy View: Hold down L1 + R1, then press Triangle, Circle, Triangle, Circle
One-Hit Wrecks: Hold down L1 + R1, then press Triangle, Triangle, Square, Square
Unlock Red Brick Car: Hold down L1 + R1, then press Circle, Circle, Triangle, Square.
Beat the Clock:
During timed missions the clock will not start until you get into your car. To get a head start simply run to the area you need to get to and then steal a car or visit a phone booth to get a car and continue the mission.
Unlock Itchy and Scratchy Cartoon:
Collect all the cards in every level of the game to unlock an episode of Itchy & Scratchy
Unlock Multiplayer Racing Game:
Collect all the cards in just one level to unlock the multi-player racing mini game.
Holiday Look:
Change your system's internal clock to the dates for Thanksgiving, Halloween and Christmas to experience a different game look.