Select the "Settings" option at the main menu, then select the "Cheat Codes" option. Then, enter one of the following codes to activate the corresponding cheat function. The codes are case-sensitive:

IMALAZYBEEOTCH - Unlock single-player levels
F3ARM3 - God Mode
ALLAMO - All ammunition
MYLOCATION - Toggle location stats
P33kaB00 - Cinematics can now be skipped
EBpwnz - Electronics Boutique content unlocked
BESTBUYpwnsYou - Best Buy content unlocked
GameStopPwnage - GameStop content unlocked
TRUPwned - Toys R Us content unlocked
FuturePwnage - Future Shop content unlocked
PwnageMart - Walmart content unlocked
YouGotGroove - Groove content unlocked
TargetingYou - Target content unlocked
ShhItsaSecret - Secret content unlocked

Press [~] during game play in single-player mode to display the console window. Then, enter one of the following codes to activate the corresponding cheat function:

god - God mode
ghost - No clipping mode
fly - Flight mode
walk - Disable flight and no clipping mode
loaded - All weapons
allweapons - All weapons
allammo - 999 ammunition for all weapons
fov  - Set field of view (default is 70)
invisible <0 or 1> - Toggle invisibility
behindview 0 - First-person view
behindview 1 - Third person view
suicide - Suicide
addbots  - Bots in multi-player game
summon VehicleGame.WeaponEnergyCore - Spawn WEC; for upgrading weapons