If you haven't got time to play through the game to unlock the Strikes, Costumes and FMV sequences then enter the corresponding code at the 'Main' menu.

Unlock ALL Strikes:
At the 'Main' menu press Triangle, Circle, Triangle, Square, Triangle, Circle, L1, R2.

Unlock ALL Costumes:
At the 'Main' menu press Triangle, Circle, Triangle, Square(3), L1 + L2.

Unlock ALL Cerebro Files and FMV Sequences:
At the 'Main' menu press Triangle, Circle, Triangle, Square(3), R1 + R2.

At the 'Main' menu press Triangle, Circle, Triangle, Square, Triangle, Circle, L1 + R1 to unlock level select and ALL challenges. Enabling this code though will cause the following.

1) You no longer get Dog Tags for Stealth attacks which prevents you from advancing to a higher strike level (collect ALL the Dog Tags you need before using the cheat).

2) Files will be marked with an 'X' when you save a game in which the 'Level Select' code has been used.

If you feel you need the help of the 'cheating' variety to progress in the game then enter this code at the 'Main' menu by pressing Triangle(2), Circle(2), Square(2), Circle(2), L1 + R1 + L2 + R2. To access the 'Cheats' option during gameplay press 'Pause'.