Various Unlockables in Need for Speed Most Wanted:
These codes must be entered at the Press Start screen using the d-pad.

Unlocks Castrol SYNTEC verion of the Ford GT - Left, Right, Left, Right, Up, Down, Up, Down
Unlocks Burger King Challenge in challenge series - Up, Down, Up, Down,Left, Right, Left, Right

Unlockable Cars in Need for Speed Most Wanted:
Aston Martin DB9 - Beat Blacklist Boss #7
Audi A3 3.2 Quattro - Beat Blacklist Boss #15
Audi A4 3.2 FSI Quattro - Beat Blacklist Boss #14
Audi TT 3.2 Quattro - Beat Blacklist Boss #15
BMW GTR (Race version) - Beat Blacklist Boss #1
Cadillac CTS - Beat Blacklist Boss #12
Chevrolet Cobalt SS - Automatic
Corvette C6 - Beat Blacklist Boss #5
Corvette C6.R - Complete 100% of the game
Dodge Viper SRT 10 - Beat Blacklist Boss #6
Fiat Punto - Automatic
Ford GT - Beat Blacklist Boss #4
Lamborguini Gallardo Beat Blacklist Boss #6
Lamborguini Murciélago - Beat Blacklist Boss #4
Lexus IS300 - Automatic
Lotus Elise - Beat Blacklist Boss #8
Mazda RX-7 - Beat Blacklist Boss #9
Mazda RX-8 - Beat Blacklist Boss #12
Mercedes-Benz CLK 500 - Beat Blacklist Boss #8
Mercedes-Benz SL 500 - Beat Blacklist Boss #11
Mercedes-Benz SLR McLaren - Beat Blacklist Boss #3
Mitsubishi Eclipse - Beat Blacklist Boss #14
Mitsubishi Lancer Evolution VIII - Beat Blacklist Boss #11
Mustang GT - Beat Blacklist Boss #12
Pontiac GTO - Beat Blacklist Boss #10
Porsche 911 Carrera S - Beat Blacklist Boss #7
Porsche 911 Turbo S - Beat Blacklist Boss #5
Porsche Carrera GT - Beat Blacklist Boss #3
Porsche Cayman S - Beat Blacklist Boss #10
Renault Clio V6 - Beat Blacklist Boss #13
Subaru Impreza WRX STi - Beat Blacklist Boss #9
Toyota Supra Beat Blacklist Boss #13
Vauxhall Monaro VXR - Beat Blacklist Boss #10
Volkswagen Golf GTI - Automatic

More Money:
If you have a Need for Speed Underground 2 file on your memory card you'll get an extra $10,000.

Easy Money when You Sell a Car:
Before you sell a car, go to a One-Stop Shop and reset all the exterior body parts (body kit, wheels, spoiler, hood, etc.) to stock. You will get a trade-in credit for the old custom parts and it will not lower the car's value when you sell it in the Safe House.