Cheat: 1 Million Dollars

On the PDA's faction screen enter the following code on the D-pad: Right, Down, Left, Up, Up, Left, Down, Right. You'll hear a sound that confirms the code has been added correctly. You'll now have a million bucks to waste as you please.

Cheat: Invincibility

On the PDA's faction screen, enter Up, Down, Up, Down, Left, Right, Left, Right on the D-Pad. You'll hear a sound that confirms the code has been added correctly.  Now you and your current vehicle will be impervious to damage.

Cheat: Unlimited Ammo

Go to the PDA's faction screen and enter the following code on the D-pad: Right, Left, Right, Right, Left, Right, Left, Left. You'll hear a click and you'll have unlimited ammo.