During Gameplay enter the following. Note: Cheats other than the Classic Wolverine Costume will disable earning Achievements.
Cheat Effect
X,A,A,X,Y,Y,X,B,B,X,R3 Undying (You will lose health but you'll never die)
Y,X,X,Y,B,B,Y,A,A,Y,R3 Infinite Rage
A,A,X,X,Y,Y,B,B,Y,Y,X,X,A,A,R3 Faster Enemy Reflex (Every kill you'll gain double reflex)
A,X,B,X,A,Y,A,Y,A,X,B,B,X, R3 Unlocks Classic Wolverine Costume

X-Men Origins: Wolverine Unlockables
Achievements

Complete each achievement to get the allotted gamerscore.
Unlockable How to Unlock
Getting Started (10) Killed 100 enemies
A Day's Work (20) Killed 500 enemies
What I Do Best (30) Killed 2000 enemies
You Can't Hide (20) Lunged to 250 enemies
Lunge (10) Lunged to 25 enemies
Pounce (15) Lunged to 100 enemies
Piggy Back Ride (10) Lunged to a W.E.N.D.I.G.0 prototype's back
Quick Killer (10) Quick Killed 1 enemy
Efficient Killer (15) Quick Killed 20 enemies
Perfect Killer (20) Quick Killed 3 enemies in a row
Drop Dead (10) Killed 10 enemies by throwing them off high areas
Apprentice (10) Raised One Combat Reflex to Master Level
Samurai (25) Raised All Combat Reflexes to Master Level
Mutant Lover (15) Raised one Mutagen to level 3
Astonishing (20) Found 1/2 of all Dog Tags in the game
Devil's Brigade (30) Found all Dog Tags in the game
Defensive (10) Performed 1 Counter move
Untouchable (20) Performed 25 Counter moves
Catch! (10) Killed 1 enemy with a reflected projectile
Boomerang (20) Killed 25 enemies with a reflected projectile
Aerial Assault (10) Performed 10 Air Grabs
Ultimate Wolverine (15) Fought 4 W.E.N.D.I.G.0 prototypes at the same time and defeated them at Alkali lake.
Hot Potato (20) Light 20 enemies on fire
Shotgun Epic Fail (15) Killed 25 Ghosts with their own weapon
James Howlett (15) Performed a Wolverine to Wolverine Lunge
WoW! (15) You feel cold as you examine the skeleton and read the name "Arthas" etched into the nearby sword
Aerial Master (15) Got 6 enemies airborne at once
Fully Loaded (35) Maxed out all upgrades
Slice n' Dice (15) Killed 6 enemies with a single attack
Found! (15) You found a mysterious hatch!
Slaughter House (15) Dismembered 100 enemies
Blender (25) Killed 200 enemies with Claw Spin
Walking Death (50) Beat the game on Hard Difficulty
Heightened Senses (20) Killed 200 enemies in Feral Sense
Environmentally Friendly (15) Killed 10 enemies using objects in the environment
Whatever it Takes (20) Killed 30 enemies using objects in the environment
Bloodlust (20) Killed 50 enemies while in Berserker mode
Weapon X (25) Killed 150 enemies while in Berserker mode
The Cake (15) You found the cake, yummy!
Bar Fight (30) Defeated Victor Creed (Sabretooth)
Spillway Escape (30) Escapes from Weapon X
Helicopter Ride (30) Defeated David Nord (Agent Zero)
Stick Around (10) Impale Victor Creed outside the Bar
Threading the Needle (15) Flew through the 0 ring in the Sentinel Boss Battle
Fallen Sentinel (30) Defeated the Sentinel Mark 1
Achievement - Clean Up On All Aisles (10G) Destroyed all objects in the grocery store fight with Fred Dukes (The Blob)
The Dead Pool (50) defeated weapon 11 (deadpool)
The Villiage (30) Completed the jungle mission
52 pick Up (30) defeated Remy LeBeau (gambit)
Put Up Your Dukes (30) Defeated Fred Dukes (the Blob)
New Costumes

Collecting the action figures throughout the game earns you challenges where you face a Wolverine in a different costume. Beat the challenge to unlock that particular costume.
Unlockable How to Unlock
Blue/Yellow Wolverine Classic Wolverine Challenge complete
Brown/Yellow Wolverine Legendary Wolverine Challenge complete
X-Force Costume X-Foce Wolverine Challenge complete

Hard difficulty

Beat the game.