Livery Codes - From the main GRID menu go to Options > Bonus Codes > Enter Code and enter the bonus Code in the space onscreen.

Password Effect

TUN58396 All drift cars
MUS59279 All muscle cars
F93857372 Buchbinder 320si Livery
M38572343 Free Pagani Zonda R
P47203845 Play.com Livery
G29782655 Unlock a BMW 320si for Use in Grid World and Raceday. Locked to Gamestation Livery

Unlockables - Complete each achievement to get the allotted gamerscore.

1st and 2nd at Global (25) Get a 2-1 at Global Level
Airborne (15) Get the car airborne for 1 second

Back To Front (10) Cross the finish line in first place in reverse
Beat Codies (30) Beat the developer or anyone who has beaten the developer online

Car Wreck (5) Cause insane damage to your car
City Slicker (20) Race in every city
Combo King (20) Get a x50 Drift Multiplayer
Corporate Power (10) Fill all your sponsor slots

Driver for Hire (10) Race for a team from every region

Filthy Rich (25) Earn enough to buy a brand new Lamborghini Murcielago GTR
First Wheels (5) Buy your first car
First Win! (10) Win your first race
First Xbox LIVE Win (10) Win your first ranked Xbox LIVE race
Five Xbox LIVE Wins (30) Win 5 ranked Xbox LIVE races
Flashback & Win (5) Use the Flashback feature and win the race
Full Rep (10) Earn the full reputation available on EXTREME difficulty

Gentleman Driver (30) Win an entire GRID World Event without making contact with other cars
Global License (20) Unlock your Global License
Globe Hopper (30) Race at every location
Gotta Drive 'Em All (30) Drive every car 30 points

Hard Charger (20) Win a 12 car race starting from the back of the Grid
Head 2 Head (30) Win your first Head 2 Head race
High Mileage (30) Drive 750 miles in a single car
Hire & Fire (10) Hire a new teammate with a higher rank than your current one
Hot Lap (20) Beat the original lap record on any track

Keep Drifting (10) Drift your car for 5 seconds
Keep Rolling (10) Roll your car 20 times

Last Man Standing (20) Be the last survivor of a single player Demolition Derby
Le Mans Legend (30) Win a Le Mans 24 Hour race on Pro Mode.
Le Mans Rookie (15) Complete your first Le Mans 24 hour race
Long Haul (40) Drive a total of 1000 miles

New Kid on the Block (5) Complete your first race

Online Elite (30) Obtain the 'Elite' rank in the Xbox LIVE game mode.
Online Legend (50) Obtain the 'Legend' rank in the Xbox LIVE game mode.

Power Seller (25) Sell a car for more than you paid for it

Record Breaker (10) Complete a lap of Okatama Grand Circuit in under 90 seconds
Road Block (10) Be involved in a 3 car pile-up

Seasoned Pro (30) Win all Event Trophies
Short Haul (30) Drive a total of 500 miles
Speed Demon (10) Reach 200mph in any car in a GRID World race
Spin & Win (10) Complete a 360º spin and still win the race
Stick Shift (10) Win a race using manual transmission
Sunday Drivers (30) Finish a race at least one lap ahead of the rest of the field in GRID World or Race Day

Team Win (20) Take your team to win its first Event
Top of Team Leaderboard (35) Top the Team Leaderboard
Top of the Tree (35) Top the Driver Leaderboard
Touge King (20) Win a Touge Event on EXTREME difficulty

When Will I Be Famous? (20) Get onto a Hall of Fame Leaderboard
Winning Streak (15) Win all races in an Event

You Again? (20) Lap an opponent in a 12 car GRID World race

Ninja Difficulty - To unlock Ninja Difficulty, get every trophy and complete every head-to-head race in Grid World

Complete all the global events in 1st place to unlock the final Head 2 Head with Ravenwest. After winning this final race you will unlock all the cheats. To activate, go to Main Menu> Options > Bonus Codes. From there, select the cheats you wish to activate.

Unlock the Grid gamer picture by topping both Team and Driver Leaderboards.