Syphon Filter Cheats
For unlimited weapons press start, highlight the Weapons icon, and press and HOLD- Right+L2+R2+Square+X+O and you should enter the weapons inventory with all the weapons for the stage you are in.
Now for the "Level Select" code press start go in the Options menu go to "Mission Select" then Press and HOLD, Left+L1+R1+Select+Square+X, this might be kind of hard to do but I tested them and they worked.
Ultra Guns: Press start go to the map and press and hold right, R1, L2, X. You should hear a laugh activating the code. This code is like the super 9mm code but it affects all the weapons.
Super 9mm: pause the game, highlight the weapons menu, highlight silenced 9mm, then simultaneously press and hold Left, L1, R2, square, select and X, you should hear Gabe either say Damn or Understood, if he says "damn" the guns will take 2x as less lives, if he says "understood" the guns will kill an enemy in one shot.
Movie theater: pause the game during the Georgia Street level, highlight the map menu, then simultaneously press and hold Right, L2, R1, and X
Hard difficulty level: at the title screen, highlight New Game, then simultaneously press and hold Left, L1, R2, Select, square, circle, and X gabe should say Damn it.