Player Cheats:

During gameplay press the following:

Swimming Ability:
R2, R2, L1, CIRCLE, LEFT, RIGHT, UP, R2

Armor:
R1, R2, L1, X, Left, Down, Right, Up, Left, Down, Right, Up

All Weapons #1 
Press R1, R2, L1, R2, Left, Down, Right, Up, Left, Down, Right, Up 
Note: This does not unlock special weapons such as the 
      chainsaw, which can be found during the game. 

All Weapons #2 
R1, R2, L1, R2, Left, Down, Right,Up, Left, Down,Down,Left 

All Weapons #3 
R1, R2, L1, R2, Left,Down,Right,Up,Left,Down,Down,Down 

Free Tank:
O(6), R2, L2, L1, triangle, circle triangle.

Full Health 
R1, R2, L1,Circle,Left,Down,Right,Up,Left,Down,Right,Up 

Ladies Man (certain women follow you)
Circle,X,L1,L1,R2,X,X,Circle,Triangle

Commit Suicide 
Right,L2,Down,R1,Left,Left,R1,L1,L2,L1 

Speed Up Time 
Circle,Circle,L1,Square,L1,Square,Square,Square,L1,Triangle,Circle,Triangle 

Slow Down Time 
Triangle,Up,Right,Down,Square,R2,R1 

Weather Cheats:

During game play press the following:

Sunny Weather
R2, X, L1, L1, L2, L2, L2, Down

Cloudy Weather
R2, X, L1, L1, L2, L2, L2, Triangle

Very Cloudy Weather
R2, X, L1, L1, L2, L2, L2, Square

Stormy Weather
R2, X, L1, L1, L2, L2, L2, Circle

Foggy Weather
R2, X, L1, L1, L2, L2, L2, X