Driver: Parallel Lines - PS2 & Xbox
Cheat mode
Pause the game and select the "Settings" option. Then, select the "Cheats" option and enter one of the following codes to unlock the corresponding cheat option, which can then be toggled on or off:

Infinite Ammo
Enter "GUNBELT" as a code.

Kingdom Hearts 2 - PS2
Remain in transformed state
If you are in a transformed state, ride a skateboard to stay in your transformed state, even if your Drive gauge goes to zero. However, if the gauge is already at zero and you get off the skateboard, you will return to your regular form.

Metroid Prime: Hunters - DS
Sound Test option
Defeat Gorea's second phase to unlock the "Sound Test" option.

Suikoden V - PS2
Byakuren
An easy way to get Byakuren (the giant snake that attacks you when you cross the bridge in your Headquarters) is to have Levi (the magician) in your party and defeat him. Afterwards he will join your Star Of Destiny tablet.

The Elder Scrolls IV: Oblivion - X360 & PC
Infinite iron arrows
Go to the Bloodworks in the arena and find the gladiator that is practicing with his bow on a target. Stand close by him and when there are five to ten arrows in the target, take them before he does. He will just continue shooting when you move out of the way. This is an unlimited source of iron arrows, which can be sold to almost any merchant and therefore also makes an unlimited source of gold.

The Godfather - PS2, Xbox & PC
Full health
PS2: Pause the game and press Left, Square, Right, Circle, Right, L3.

Tom Clancy's Ghost Recon: Advanced Warfighter - X360
Mission Select
At the mission selection screen, hold LT + RT + Back and slowly press Y, RB, Y, RB, X to unlock all missions. If you entered the code correctly, you will hear a sound.