Each ending unlocks one bonus costume. There is also one secret costume.

Deputy Alex. Get the UFO Ending.
Big Rig Alex. Get the Good Ending.
ER Alex. Get the Hospital Ending.
Order Soldier Alex. Get the Drowning Ending.
Bogeyman Alex. Get the Bogeyman Ending.
Young Alex. Use the Konami Code.
Restart the game and do not press the Start button in the menu. Enter the Konami Code:
Xbox 360: ↑, ↑, ↓, ↓, ←, →, ←, →, A, B.
PS3: ↑, ↑, ↓, ↓, ←, →, ←, →, X, O.
If you entered correctly, you should hear a page flip.

Slent Hill Homecoming Costume Slent Hill Homecoming Costume Slent Hill Homecoming Costume Slent Hill Homecoming Costume Slent Hill Homecoming Costume Slent Hill Homecoming Costume Slent Hill Homecoming Costume
Classic Alex Young Alex Deputy Alex Big Rig Alex ER Alex Order Soldier Alex Bogeyman Alex

Extra Weapons

Circular Saw
To unlock the Circular saw, you just need to beat the game once (the ending doesn't matter). During your next play through the Circular Saw can be found in the garage of Shepherds' house.

Laser Pistol
To unlock the Laser Pistol, you need to beat the game with the UFO Ending. During your next play through the Laser Gun will be in Josh's/Alex's old room on top of the dresser.

Extra Cutscene

Silent Hill Shattered Memories ending To see this cut scene you must finish the game on hard difficulty or find all the drawings and photos during one completion. If you do, there will be an extra cut scene after the credits showing Alex from a first person view climbing the stairs in Shepherds' house and finding Joshua sitting on the bed, Joshua laughs and takes a picture of Alex.

Xbox 360 Achievements

Lock 'n' Load
Found Rifle
25 points
Found 1 Photo
10 points
Josh's Gallery
Found ALL Photos
50 points
Alchemilla's Finest
Defeated 1 Nurse
10 points
Eddie's Legacy
Defeated 1 Feral
10 points
Lurk No More
Defeated 1 Lurker
10 points
To The Point
Defeated 1 Needler
10 points
Split Personality
Defeated 1 Schism
10 points
Shades of James
Defeated 1 Siam
20 points
Clear the Air
Defeated 1 Smog
10 points
Creeper Reaper
Defeated 1 Swarm
10 points
Out of Order
Defeated 1 Order member
10 points
Kaufmann's Handiwork
Found 1 Serum
10 points
Health Junkie
Found all Serums
50 points
The Old Gods Haven't Left This Place
Complete game on HARD difficulty
100 points
Nursery Rhymes
Found all the Children's Drawings
50 points
Six Feet Under
Defeated Sepulcher
50 points
Blood Donor
Defeated Scarlet
50 points
Catch Your Breath
Defeated Asphyxia
50 points
Head Above Water
Defeated Amnion
50 points
Rising Tension
Found Circular Saw
25 points
Science Fiction
Found Laser Pistol
25 points
Achieved Ending 1
50 points
In Water
Achieved Ending 2
50 points
Achieved Ending 3
50 points
Intensive Care
Achieved Ending 4
50 points
No Dogs Allowed
Achieved Ending 5
50 points
Alex ended his mother's suffering
20 points
Alex could not end his mother's suffering
20 points
Alex Forgives his father
20 points
Angela's Choice
Alex does not forgive his father
20 points
Now About Those Drinks
Saved Wheeler
25 points