All codes require you to be in DEBUG mode. 
Press F9 and a place to type stuff will appear at the top of the screen. 

To turn on debug mode, type in BANGUNSNOTGAMES. 
This will make you invulnerable. 

These cheat codes are typed into the F9 input line:

CodeResult 
BOO Cluster of explosions 
CRINKLES  Turn Crinkles on/off 
DARCI     Control Officer D'arci 
ROPER     Control Roper 
FADE #    Sets fog fade level where # is any number 
WORLD     Select music 
AMBIENT # # #   Set ambient light (R,G,B) 
WIN Win the level 
LOSELose the level 
CCTVEverything turns fluorescent green 
TELW #    Go to important game point # 
TELSSave a waypont on map 
TELRReturn to saved waypoint 


The rest are simple key presses. Just press the corresponding keys to make 
these happen:

Key Result 
Q   Show car paths 
W   Make rain ripples 
E   Make random vehicle 
R   Make explosive barrell 
I   Show pedestrian walking areas 
[   Toggle enemy view 
]   Toggle enemy view 
P   Enemy view on/off 
;   Slow motion 
'   Pause action 
>   Fart smoke 
/   Stealth Debug 
CTRLShow statistics 
G   Move forward 10 feet or onto ledge 
J   Coordinates grib show 
L   Create light 
F11 Clouds on/off 
F12 Creates game weapons 
F3  Exits game 
Keypad 7  Select game effect 
Keypad 5  Execute game effect 
Keypad 3  Weird orange fog