Start by pressing "ALT+J+H" to enter a code box.

Type these codes in your code box:

Faerie Ha Ha!!!:
This enables your username to be accessed by anyone.

Make It Snappy:
Do a robbery of 14 party hats. 

Winner Loser:
This code gives your opponent a slight advantage in the batteldome.

Clock Work:
A mad clock will appear in front of your screen and your pet will be changed into a morphed Meerca.

These codes only work right after you login on your account:

Let's do it!:
First go to games section and enter "kldgst" in the search box. Only one game will appear now click on it. The page will load with one thing on it! It will be a flash movie of "Pokemon: Orange Islands." Now click here to go to the Secret Dungeon . Then it will take you to a page with a flashing banner somewhat like this:   . Then go to the games section and you will get a Key-                                           chain!!!

Secret Dungeon of MWAHAHAHA People:
Go to Krawk Island and click the very south by west corner. You will end up in Lego's Lair where he will appear and you will fly with the BFI. In the background he will go quack, quack, quack each in different tones. You will eventually land on the Tokyo Tower press: Q,U,A,C,K,Q,U,A,C,K,Q,U,A,C,K. You will float elsewhere chosen at random and land in the Secret Dungeon of the MWAHAHAHA People!

Get as many items as u want:
Go to shops and click an item that you can afford and then click OK right after that you hold down ENTER and ALT for as many items as u want.....It worked for me................
                                                                                                                     Submitted by ME
 

The following is unintelligible but was sent in by candy_bri.
go to chat bored post in guilds come here hurry.
then post this 10 times mo mon mone money then press ctrl alt then 10 it will take all the money from the people that came to the bored to you

The following is unintelligible but was sent in by Money.
Give me money neopet 100000000000np

All missions unlocked:
By pushing any button to interrupt the opening sequence and quickly pushing  X, L2, Triangle, R2, Select when the title screen becomes visible. The start up screen will have a different picture to confirm correct code entry..

All special features:
By pushing any button to interrupt the opening sequence and quickly pushing  L1, L2, R1, R2, X, Select when the title screen becomes visible.

Invincibility:
By pushing any button to interrupt the opening sequence and quickly pushing  L1, R2, L2, R1, Select when the title screen becomes visible. Your first soldier will be invincible, but the remaining members of your platoon can still be harmed. This code must be re-activated every level and can be performed when pausing the game.

Bonus levels:
Upon finishing the fifteen normal levels another eight levels that take place in the desert called  GHOST RECON DESERT SIEGE  will be unlocked.

Medals:  

Purple Heart: By getting wounded or killed in action.
Bronze Star: By getting 15 kills
Silver Star: By getting 20 kills
Distinguished Service Cross: By getting 25 kills
Congressional Medal Of Honor: By getting 30 kills

Every heroe:
Finish the first twelve missions in campaign mode to unlock all twelve heroes as playable characters in quick mission and campaign modes. 

The characters which can be unlocked are Henry Ramirez, Nigel Tunney, Will Jacobs, Jack Stone, Guram Osadze, Susan Grey, Klaus Henkel, Buzz Gordon, Lindy Cohen, Astra Galinksy, Scott Ibrahim, and Dieter Munz.

By finishing (X) objective for every mission, you will unlock a new soldier. These soldiers wil have boosted stats and have their own specialist weapons. If these soldiers die, you will not be able to use them except in quick mission mode. You can also use their weapons in multi-player mode.

To activate these cheats, you have to enter some command line arguments. Make the shortcut to Half-Life point to this - "C:\Half-Life\hl.exe -dev -console" replacing c:\Half-Life with whatever directory you installed the game to.

After running the game with those arguments, you can enter a console within the game by typing the tilde "~" key. If cheats don't work at first, you'll have to type in "sv_cheats 1" at the console and cheats should be enabled for the next level that loads.

Activate the following codes by opening the console, then typing each and hitting [ENTER] after each one.

/god: God mode/invulnerability.
/noclip: No clipping mode/walk through walls.
/notarget: Deactivates any reaction from enemies until they are shot at.
/give: There's a whole plethora of things you can get with this command...