Type at the car select screen:

GLORIOUS        -  Cheats Enabled
ICECREAM        -  Play as Sweet Tooth
BIGBOY          -  Play as Minion

Type while playing:

GLORIOUS        -  Cheats Enabled
DIVINE          -  God Mode
ALLUCANEAT      -  Eternal Life
DOUBLEDOWN      -  Supercharged Weapons
HOLYSMOKES      -  Infinite Weapons
SLAMFEST        -  Super Slam
GIMMEMORE       -  Weapons Added
2HOT            -  Homing Napalm
CUSUCKA         -  Mega Guns
FRAMERATE       -  Display framerate

While playing, press these keys in rapid succession:

D,U,R,L,U,U,D,D -  Soul sold (trade weapons for health)
L,R,U           -  Freeze Burst
R,L,D           -  Mine
R,L,U           -  Napalm
U,U,R           -  Shield
U,U,L           -  High Jump
L,R,D           -  Rear Attack
R,D,L,U         -  Cloaking
U,D,U,U,Space   -  Minion Attack

Type at the Level Select screen in multi-player mode:

DASBAK          -  Net Cheats Enabled
SLEUTH          -  Sneak Peeks
JMSWAMP         -  Suicide Swamp Level
TMBURBS         -  Cyburbia Level
TMROOF          -  Rooftops Level