NASCAR 08 Codes -

Unlock Bonus Wal-Mart Car
Enter "WALMART EVERYDAY" as a password at the cheat code section in the menu to unlock bonus Wal-Mart car.

Unlock All Fantasy Drivers
Enter "RACE THE PACK" as a password at the cheat code section in the menu to unlock all fantasy drivers.

Unlock All Chase Mode Cars
Enter "CHECKERED FLAG" as a password at the cheat code section in the menu to unlock all chase mode cars.

Achievements
Complete each achievement to get the allotted gamerscore:

3 Wide (10) - Earn Three Gold Medals in "The Chase" Mode.
All Or Nothing (100) - Reach 100% Game Progress.
Badge Of Honor (10) - Complete a Driver Badge.
Chase Champion (100) - Win a NEXTEL Cup in "The Chase" Mode.
Chase For The Cup (25) - Win a Championship in Season Mode using the Car of Tomorrow Series Full Schedule.
Craftsman Tools Reward (50) - Save a Craftsman Tools Car Setup at any Track.
Cross Country (100) - Drive 5,000 Total Miles.
Custom Car Creator (10) - Complete a Custom Car for all racing series.
Earn Your Stripes (25) - Earn a License in "The Chase" Mode.
Full Throttle (100) - Complete a 100% Length Race in Race Now or Season Mode.
Heavy Medal (10) - Win a Medal in "The Chase" Mode.
Independent Contractor (25) - Earn a Contract in "The Chase" Mode.
Keep On Truckin' (10) - Win a Craftsman Truck Series race.
Licensed To Drive (25) - Complete all Licenses in "The Chase" Mode.
National Hero (10) - Win a NASCAR National Series race.
Online Horsepower (25) - Win an Online Race.
Pay The Bills (100) - Complete all Contracts in "The Chase" Mode.
Play It Again, Sam. (10) - Save a Race Replay.
Sprint Reward (75) - Win a NEXTEL Cup in Season Mode using the NEXTEL Cup Series '07 Schedule.
Today Or Tomorrow? (10) - Win a NASCAR Car of Tomorrow race.
Toyota Reward (50) - Complete all Toyota Challenges.
Trade Your Setup (10) - Upload a Car Setup to EA Locker.
We Don't Need No Badges! (100) - Earn all Driver Badges.
We're Talkin' About Practice (10) - Record a Lap in Toyota "Test and Tune" Mode.