To unlock all Chase Mode cars, insert "Checkered Flag" (minus the quotes) in the cheat menu.
To unlock the EA Sports Stock Car, insert "EA Sports Car" (minus the quotes) in the cheat menu.
To unlock all in-game fantasy drivers, enter "Race the Pack" (minus the quotes) at the cheats menu.
To unlock the Wal-Mart car and track, head to the in-game cheats menu and insert the code Walmart Everyday.