All Weapons:
For all weapons & maximum ammo, call up the inventory screen & press one of the following key sequences (depending on how you set your controls) -
Default Controls L1, Triangle, R2, L2, L2, R2, Circle, L1.
Control Method 2 Triangle, Circle, R2, L2, L2, R2, L1, Triangle.
Control Method 3 Triangle, R1, R2, L2, L2, R2, L1, Triangle.

Handstand:
When Lara is hanging on a ledge, hold the Walk button & press Up to do a handstand.

Level Skip:
While playing, call up the inventory screen & press one of the following key sequences (depending on how you set your controls) -
Default Controls L2, R2, L1, Circle, Triangle, L1, R2, L2.
Control Method 2 L2, R2, Triangle, L1, Circle, Triangle, R2, L2.
Control Method 3 L2, R2, Triangle, L1, R1, Triangle, R2, L2.

Unlimited Ammo:
If you win the game & reload any saved level you'll have all weapons, unlimited ammo & more enemies to defeat.

Darth Vader's Head:
Pause the game & go into inventory. Then press X, X, Circle, Triangle, Triangle, Circle, Circle, Circle, Circle, Square, Square, Square. If entered right, Lara will say 'May the force be with you, Luke' & her head will be Darth Vader's.