When in combat, hold down CTRL-ALT-SHIFT and type:
 
CIA         - Unlimited weapons
COLDMISER   - Heat Tracking on/off
DEI         - Prints the letters FEIF on the top of the screen
DORCS       - Meet the Dor(k)s!  See MW2 Programming team!
ENOLAGAY    - Nuke (Work only once during simulation)
TLOFRONT    - Rear view camera faces front
HANGAROUND  - Linger on battlefield after mission over
ICANTHACKIT - End Mission
IDKFA       - End Mission
LAIRDO      -
MEEPMEEP    - Time compression key enabled
UNMEEPMEEP  - Time compression disabled
MICHELIN    - Look on the mech parts now!