When you play in Career mode you will challenge the 5 Kings (Showdown, Drift, Drag, Speed and Grip), when you beat them you will unlock their car.

Unlock 1965 Pontiac GTO (Nate Denver):
Beat Speed King in Career mode.

Unlock 1995 RX-7 (Aki Kimura):
Beat Drift King in Career mode.

Unlock 2006 Mustang GT (Karol Monroe):
Beat Drag King in Career mode.

Unlock 2008 Evo X (Ryo Watanabe):
Beat Showdown King in Career mode.

Unlock 2008 M3 E92 (Ray Krieger):
Beat Grip King in Career mode.

These codes are entered at the 'Enter Code' menu which is found by going to 'Options' and then 'Career Mode'. Some of these codes can only be used once so it is advised that you disable the 'Auto-Save' option so you can revert the game back to it's original setting.

Unlock Everything in the Game:
Enter the password 'UNLOCKALLTHINGS' to unlock ALL maps, cars etc.

Unlock ALL Bonuses:
Enter the password 'MASTERCODE' to unlock ALL the bonuses in Career mode.

Unlock Chevelle SS:
Enter the code 'HORSEPOWER' to unlock the Chevelle SS in Career mode.

Unlock Audi TT 3.8 Quattro:
Enter the code 'ITSABOUTYOU' to unlock the Audi TT 3.8 Quattro in Career mode.

Unlock Coke Zero Volkswagen Golf GTI:
Enter the code 'ZEROZEROZERO' to unlock the Coke Zero Volkswagen Golf GTI In Career mode.

Unlock Mitsubishi Lancer Evolution:
Enter the code 'MITSUBISHIGOFAR' to unlock the Mitsubishi Lancer Evolution in Career mode.

Unlock Energizer Lithium Dodge Viper SRT10:
Enter the code 'WORLDSLLONGESTLASTING' to unlock the Energizer Lithium Dodge Viper SRT10 in Career mode.

Unlock Castrol Syntec Decal:
Enter the code 'CASTROLSYNTEC' to unlock the Castrol Syntec decal in Vinyls.

Unlock Energizer Lithium Decal:
Enter the code 'ENERGIZERLITHIUM' to unlock the Energizer Lithium decal in Vinyls.

Unlock 5 Free Repair Markers:
Enter the password 'SAFETYNET' to get 5 free repair markers in Career mode (this password can only be used once).

Unlock Extra $2,000:
Enter the code '1MA9X99' to get an extra $2,000 in Career mode (this password can only be used once).

Unlock Extra $4,000:
Enter the code 'W2iOLLO1' to get an extra $4,000 in Career mode (this password can only be used once).

Unlock Extra $8,000:
Enter the code 'L1iS97A1' to get an extra $8,000 in Career mode (this password can only be used once).

Unlock Extra $10,000:
Enter the code 'CASHMONEY', 'REGGAME' or '1Mi9K7E1' to get an extra $10,000 in Career mode (this password can only be used once).

To get a bonus 3 extra Repair Tickets and a Total Repair Ticket have a Need For Speed Carbon memory save on your PS3. You'll know if you've recieved the extra bonus because you'll see a message on your screen thanking you for playing previous Need for Speed titles.