For all weapons and maximum ammo, call up the inventory screen and 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

When Lara is hanging from a ledge, hold the WALK button and press UP to do a handstand.

While playing, call up the inventory screen and 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

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