In L.A. Noire for the PS3 and Xbox 360, there are several unlockable outfits you can attain by doing certain things, or reaching certain points in the game.
Here is the list of unlockable outfits, and what you need to do to unlock them.
Chicago Lightning – Sign up for the Rockstar Social Club – Increases your accuracy with shotguns and machine guns
Golden Boy – Given to you when you start the Traffic Desk
Hawkshaw – Unlocked at Rank 18 – Allows you to take more damage
Sunset Strip – Unlocked at Rank 8
Sword of Justice – Unlocked at Rank 3
The Outsider – Unlocked at Rank 13
These outfits were originally only given out as pre-order bonuses from various different vendors, but the makers of the game have officially stated that they intend for all of them to be available at some point in the future via DLC purchase.
The Broderick – Pre-order bonus from Amazon. Increases melee damage and damage resistance.
The Sharpshooter – Pre-order bonus from Best Buy in the US and Canada, and Zavvi in the UK. Increases accuracy with pistols and rifles.
Button Man – Pre-order bonus in the USA, Canada, and Australia from GameStop & EB Games, and GAME in the UK. Requires you to complete the Badge Pursuit Challenge by collecting 20 hidden shields. Grants all weapons extra ammunition while worn.