Unlockables:

Enter the following codes at the "press start" screen. Directionals should be inputted with the d-pad.
Porsche Cayman
L1, R1, R1, R1, Right, Left, Right, Down

Castrol Ford GT
Up, Down, Up, Down, Left, Right, Left, Right

Free Upgrades
Up, Up, Down, Down, Left, Right, Up, Down.

Burger King Challenge
Up, Down, Up, Down, Left, Right, Left, Right

Extra Money
Start a new career with a save file from NFS: Underground 2 file on it. You get some extra cash to start off.