Half-Life 2: Full ammunition:
Press Y, B, A, X, RB, Y, X, A, B, RB during game play.
Portal: Create box:
Press Down, B, A, B, Y, Down, B, A, B, Y during game play.
Portal: Fire energy ball:
Press Up, Y2, X2, A2, B2, Up during game play.
Portal: Fire rocket projectile:
Press Up, Y2, B2, A2, X2, Up during game play.
Portal: Portalgun ID 0
Press Up, Left, Down, Right, Up, Left, Down, Right, Y2 during game play.
Portal: Portalgun ID 1
Press Up, Left, Down, Right, Up, Left, Down, Right, X2 during game play.
Portal: Portalgun ID 2
Press Up, Left, Down, Right, Up, Left, Down, Right, A2 during game play.
Portal: Portalgun ID 3
Press Up, Left, Down, Right, Up, Left, Down, Right, B2 during game play.
Portal: Portal placement anywhere
Press Y, A, B, A, B, Y2, A, Left, Right during game play.
Portal: Upgrade Portalgun
Press X, B, LB, RB, Left, Right, LB, RB, LT, RT during game play.
Achievements:
Complete the following achievements to unlock Xbox Live Gamerscore points.
Bone Breaker 5 points: Kill 30 enemies with thrown physics objects.
Deadly Harvest 5 points: Kill an enemy by planting a hopper mine.
Hack Attack 5 points: Kill five enemies with a Manhack.
Hot PotatOwned 10 points: Kill a Combine soldier with his own grenade.
Conservationist 5 points: Kill five enemies with the same energy ball.
Think Fast 10 points: Kill an Elite Soldier with his own energy ball.
Grave Robber 5 points: Steal a Zombine's grenade.
Zombie-que 5 points: Use flares to light 15 zombies on fire.
Malcontent 5 points: Escape the apartment block raid.
What cat? 5 points: Break the mini-teleporter in Kleiner's lab.
Trusty Hardware 5 points: Get the crowbar.
Barnacle Bowling 5 points: Kill five barnacles with one barrel.
Anchor's Aweigh 5 points: Get the airboat.
Heavy Weapons 5 points: Get the airboat's mounted gun.
Vorticough 13 points: Discover the hidden singing vortigaunt cave in chapter Water Hazard.
Revenge 10 points: Destroy the hunter-chopper in Half-Life 2.
Blast from the Past 10 points: Find the HEV Suit Charger faceplate in Eli's scrapyard.
Zero-Point Energy 5 points: Get the Gravity Gun in Black Mesa East.
Two Points 2 points: Use DOG's ball to make a basket in Eli's scrapyard.
Zombie Chopper 25 points: Play through Ravenholm using only the Gravity Gun.
OSHA Violation 5 points: Kill 3 enemies using the crane.
Targetted Advertising 5 points: Pin a soldier to the billboard in chapter Highway 17.
One Man Army 5 points: Destroy six gunships in Half-Life 2.
Keep Off the Sand 20 points: Cross the antlion beach in chapter Sandtraps without touching the sand.
Bug Hunt 10 points: Use the antlions to kill 50 enemies.
Flushed 5 points: Kill an enemy with a toilet.
Warden Freeman 10 points: Survive the second turret standoff in Nova Prospekt.
"Radiation Levels Detected" 5 points: Get through the toxic tunnel under City 17 in Half-Life 2.
Plaza Defender 10 points: Survive the generator plaza standoff in chapter Anticitizen One.
Counter-Sniper 5 points: Kill all of the snipers in City 17.
Fight the Power 10 points: Shut down the supression device by disabling its generators.
Giant Killer 10 points: Survive the rooftop strider battle in the ruins of City 17.
Lambda Locator 15 points: Find all lambda caches in Half-Life 2.
Watch Your Head 5 points: Make it to the bottom of the Citadel's main elevator shaft in one piece.
Containment 5 points: Contain the Citadel core.
Pacifist 10 points: Contain the Citadel core without killing any stalkers.
Car Crusher 5 points: Use the cars to squash 15 antlions in Episode One.
Elevator Action 10 points: Survive long enough to get on the parking garage elevator.
Live Bait 10 points: Help Alyx snipe 30 enemies in Episode One.
Attica 5 points: Destroy the gunship in the hospital attic.
Citizen Escort 15 points: Don't let any citizens die when escorting them to the escape train.
Escape From City 17 20 points: Escape City 17 with Alyx.
The One Free Bullet 40 points: Beat Episode One firing exactly one bullet. Grenade, crowbar, rocket, and Gravgun kills are okay.
Acid Reflex 5 points: Kill an acid antlion worker.
Get Some Grub 20 points: Squish every antlion grub in Episode Two.
Pinata Party 5 points: Find and break every web cache in Episode Two.
Into the Breach 5 points: Help Griggs and Sheckley hold off the antlion invasion inside the mine shaft.
Hit and Run 5 points: Run over 20 enemies with the car in Episode Two.
Puttin' On a Clinic 15 points: Defeat the chopper in Episode Two without any misses.
Cache Checker 10 points: Find every radar cache in chapter Under The Radar.
Gordon Propelled Rocket 5 points: Unlock the rocket launcher lambda cache in chapter Under The Radar.
Pedal to the Metal 5 points: Beat DOG in a race to the White Forest base.
Little Rocket Man 30 points: Send the garden gnome into space.
Neighborhood Watch 35 points: Save all buildings outside the missile silo from destruction.
Payback 10 points: Kill a Hunter with its own flechettes.
Lab Rat 5 points: Acquire the fully powered Aperture Science Handheld Portal Device.
Fratricide 5 points: Do whatever it takes to survive.
Partygoer 5 points: Make the correct party escort submission position decision.
Heartbreaker 10 points: Complete Portal.
Terminal Velocity 5 points: Fall 30,000 feet.
Long Jump 5 points: Jump 300 feet.
Cupcake 10 points: Beat two Portal advanced maps.
Fruitcake 20 points: Beat four Portal advanced maps.
Vanilla Crazy Cake 30 points: Beat all six Portal advanced maps.
Basic Science 10 points: Earn bronze medals on all Portal challenges.
Rocket Science 20 points: Earn silver medals on all Portal challenges.
Aperture Science 40 points: Earn gold medals on all Portal challenges.
Turret 5 points: Accumulate 10 turret kills with a single turret.
Nemesis 5 points: Get five revenge kills.
Hard to Kill 10 points: Get five kills in a row without dying.
Master of Disguise 15 points: Trick an opposing medic into healing you.
With Friends Like these.. 10 points: Play in a game with seven or more players from your friends list.
Dynasty 10 points: Win 20 games.
Hardcore 15 points: Accumulate 1000 total kills.
Powerhouse Offense 5 points: Win 2Fort with a shutout.
Lightning Offense 10 points: Win Well in 5 minutes or less.
Relentless Offense 20 points: Win Hydro without giving up a capture.
Impenetrable Defense 10 points: Successfully defend Dustbowl without giving up a capture.
Impossible Defense 30 points: Successfully defend Gravel Pit without giving up a capture.
Head of the Class 5 points: Play a complete round with every class.
World Traveler 5 points: Play a complete game on every map.
Team Doctor 5 points: Accumulate 25000 heal points as a Medic.
Flamethrower 5 points: Set five enemies on fire in 30 seconds.
Atomizer 10 points: Disintegrate 15 soldiers by throwing them into a Combine ball field.
Follow Freeman 10 points: Gain command of a squad of rebels in the uprising.
Grey Matter 5 points: Get 25 headshots as a Sniper.
Camera Shy 5 points: Detach security cameras from the walls.
Friendly Fire 5 points: Knock down a turret with another turret.
Additionally there are eleven secret achievements, ten of which are currently unknown.
Defiant Achievement 5 points: At the beginning of Half-Life 2 where the carbine cop asks you to pick up the can, pick it up and hit him with it.