During play, press F9 and enter bangunsnotgames to enter debug mode. Now press F9 and enter any of the following cheats:

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

After entering debug mode, ytou can simply press the following keys during play:

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 
>           Smoke 
/           Stealth Debug 
CTRL        Show stats
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 

Level skip:
During the game, press Esc + Enter + Up. You will see the Save Game screen. Save the game, and a screen stating that you have beaten the level will appear. You can do this on every level to quickly beat the game.

Thanks to Revolution readers Remi and Vipa!