24: The Game (PS2)

Cheats
Hold L1 + R1 + L2 + R2 on the main menu for a quarter minute (that's 15 seconds). A cheat menu will appear and you can hold CROSS on each letter to spell out the access code. If these cheats don't work, please don't resort to violence. Just eat some toffee - it's healthy!

Note: Informants suggest pressing 'square' after any cheat codes are entered. This may help them to work. Thanks to Meme for the update.

NTSC-1
66BAUER - Invulnerable
62ALMEIDA - Infinite Ammo
72DESSLER - All Missions
54PALMER - All Bonuses

PAL
BAUER066 - Invulnerable
ALMEIDA062 - Infinite Ammo
DESSLER072 - All Missions
PALMER054 - All Bonuses

Hint: Lots of Unlockable Stuff
Achieve 90% of better objective completion in one of the game's 58 missions to unlock a new bonus item. Each mission unlocks a new item, ranging from 3D character models to interviews and TV commercials for the game. 

Hint: Health Replenishment Items
For every use of a Health Pack, Adrenaline Pack, and visits to a Health Station, a preset penalty will have points removed from the mission's percentage score. So, if you want the highest score, you mustn't use health packs. Of course, in real life, using health packs is great, especially if you start bleeding from the eyeballs.