Metal Gear Solid 2: Sons of Liberty/Advanced moves

In addition to their more obvious functions, some moves in MGS2 can be used for other purposes.

Rolling
Both Snake and Raiden can perform a rolling move by pressing psx: X while running. It's useful for quickly evading gunfire (especially shotguns), but in Raiden's case, it can also be used to jump small gaps (notably, the bridge leading to the Shell 2 Core). If you're playing Substance, this tactic also comes in handy on some of the VR Missions.

Hanging
With your back against any railing, press psx: T, and your character will hop over the rail and hang out of sight from enemies. Be careful though - you can't hold on forever. You can also use hanging to drop from some ledges covertly (i.e. without using the stairs), or perform pull-ups by pressing psx: L2 and psx: R2 simultaneously (which will cause your grip meter to drop faster, but 100 pull-ups will increase your strength and allow you to hang on for longer). There are also some points where there is a grabbable ledge right below another - in these cases, you can drop from the upper ledge by pressing psx: X, and quickly press psx: T to grab the next one down. Not only is this handy for getting around, but ten of these will increase your grip strength (much quicker, but far riskier, than doing pull-ups).

Peeking
With your back to the wall, you can use psx: L2 and psx: R2 to peek around corners and get a better view. This will make you slightly more obvious to enemies, but it helps when you need to monitor a troop from a distance. Also, while peeking, you can chuck grenades without exposing yourself (much).

Leaning
While in first-person mode, you can use the psx: L2 and psx: R2 buttons to lean back and forth. In addition, pressing both simultaneously will raise your aiming height, so you can shoot over some dividing walls.

Strategic Cover
While against a wall, and with any standard weapon equipped, stand at the corner and press psx: S to jump out of cover and aim your weapon as normal. Releasing psx: S will put you back in cover. Be careful about using First-Person View - it may cancel out the strategic cover, meaning that the game won't put you back around the corner when you've finished shooting.

Lockers
Lockers are a universal stealth tool. Taken at face value, you can open them and find all manner of useful items - ammo, weapons, tools, even medicine. Some lockers are locked and you'll have to find a way to open them - beat them into submission with your fists, or place a brick of C4 on them. Keep in mind that the door must be present to be able to hide yourself (or an enemy) in a locker. While inside a locker, you can press the psx: R1 button to bring yourself closer to the vent cover (so you can see better - don't push the button too fast or you'll make a noise), the psx: L2 and psx: R2 buttons to peek around and see things from a different angle, and the psx: X button to crouch out of sight of inquisitive guards (useful if there's a strike team about to look through your view port at you). Pressing psx: C will knock on the locker door and draw attention to yourself. Sometimes you can knock a guard over by opening the door while they're right next to it.