Cheat Codes:
Create a shortcut to your Call of Duty executable and add the following to the end of the command line:

+set monkeytoy 0 +set sv_cheats 1

This will enable cheats in the single-player mode. Now start the game. Press the tilde (~) key to open the console, and then enter the following:

god - Invulnerability

give health - Get full health

notarget - Enemies will ignore you

noclip - You can walk through walls

Note from xnewbie: If the console tells you that "sv_cheats are read only" after you enter a code, then try typing "setrandom sv_cheats 1". This does not work in the full game.


Cheat Codes (Full Version):
These cheats work in the full version of the game, not just the demo.

Make a shortcut to codsp.exe, then edit the properties and add the command line:

+set thereisacow 1337 +set developer 1 +set sv_cheats 1 +set monkeytoy 0

Then run the game, drop the console, and put in one of the following codes:

god - Invincibility
give all - Get all weapons, items, and ammo
give ammo - Refill ammo for all weapons
noclip - Fly through walls
notarget - Enemies ignore you