One classic cheat turns the world of GTA into one big riot! The pedestrians go crazy and attack everyone - each other, you, the police... you name it. It's even better if you also use the cheat to give pedestrians weapons.
PS2 GTA San Andreas: Down, Left, Up, Left, X, R2, R1, L2, L1
PS2 GTA 3: Down, Up, Left, Up, X, R1, R2, L2, L1
GTA 4: Dial 555-891-0011