Courtesy of IGN, and a bunch of other sites who all seem to claim these codes to be exclusive to them:
Beach Party
Pedestrians turn into girls wearing swimsuits. Vehicles are also beach style and CJ will be dressed in shorts and sandals:
UP, UP, DOWN, DOWN, SQUARE, CIRCLE, L1, R1, TRIANGLE, DOWN
Get Parachute
Puts a parachute on CJ’s back:
LEFT, RIGHT, L1, L2, R1, R2, R2, UP, DOWN, RIGHT, L1Massive Bunny Hops
CJ has the ability to bunny hop on the BMX over massive distances:
TRIANGLE, SQUARE, CIRCLE, CIRCLE, SQUARE, CIRCLE, CIRCLE, L1, L2, L2, R1, R2Maximum Muscles
Immediately bumps CJ to full muscle:
TRIANGLE, UP, UP, LEFT, RIGHT, SQUARE, CIRCLE, LEFTMonster Truck
Spawns a monster truck vehicle in your vicinity:
RIGHT, UP, R1, R1, R1, DOWN, TRIANGLE, TRIANGLE, X, CIRCLE, L1, L1Spawns a Stunt Plane
A stunt plane spawns in your vicinity:
CIRCLE, UP, L1, L2, DOWN, R1, L1, L1, LEFT, LEFT, X, TRIANGLEVehicle of Death
Any vehicle the player is using becomes invincible and gains the ability to instantly destroy anything it touches.
L1, L2, L2, UP, DOWN, DOWN, UP, R1, R2, R2