Enter the following code while playing Portal to create a cube:
Down, O, X, O, Triangle, Down, O, X, O, Triangle
At any time during game play you can give yourself an additional 25 Life Points by entering the following code in game:
Up, Up, Down, Down, Left, Right, Left, Right, Circle, X.
To restore ammo to maximum, equip the gun you want to fill up, then enter the following code during game play:
R1, Triangle, Circle, X, Square, R1, Triangle, Square, X, Circle, R1.
At any time in game play enter the following code to unlock all levels:
Left, Left, Left, Left, L1, Right, Right, Right, Right, R1.
in dustbowl, when you are blue team, change into a soldier and aim your rocket at the bottom of the gate, it may take a few tries, but sometimes the rocket will go through the fence and be able to hit the other team.
The code that you usually use to increase your health by 25 in Half-Life 2, can be used in Portal, except all it does is create a medkit that can't be sent through portals or vaporized in a fizzler. It doesn't create a gun with the reload code though.