Monochrome graphics:
At the main menu, press R1, L1, Left, Triangle, Left, Left, Left, L1.
Blurry Mode:
At the main menu, press L2, L1, R1, Square, R1, R1, R1, L1.
Chrome paint:
At the main menu, press L2, R2, Left, Square, Left, Left, Left, R2.
Unlock Ferrari 360 Spider:
At the main menu, press R2, Square, R2, Square, Triangle, L2, Triangle, L2.
Unlock Lamborgini Diablo 6.0 VT:
At the main menu, press Right, R2, Right, R2, R1, L1, R1, L1.
Unlock Porsche Carerra GT:
At the main menu, press Left, Right, Left, Right, R1, R2, R1, R2.
Unlock McLaren F1:
At the main menu, press Triangle, L1, Triangle, L1, R1, Left, R1, Left.
Unlock McLaren F1 LM:
At the main menu, press Square, L1, Square, L1, Triangle, Right, Triangle, Right.
Unlock HSV Coupe GTS:
At the main menu, press L1, L2, L1, L2, R1, Triangle, R1, Triangle.
Unlock Lotus Elise:
At the main menu, press Triangle, R2, Triangle, R2, Left, Square, Left, Square.
Unlock Ford TS50:
At the main menu, press Right, Left, Right, Left, R2, Square, R2, Square.
Unlock Aston Martin V12 Vanquish:
At the main menu, press R2, Right, R2, Right, Triangle, Left, Triangle, Left.
Unlock Mercedes CLK GTR:
At the main menu, press R2, R1, R2, R1, Left, Triangle, Left, Triangle.
Unlock Chevrolet Corvette Z06:
At the main menu, press Left, R2, Left, R2, L1, R1, L1, R1.
Unlock Ford Pursuit Mustang Cobra R:
At the main menu, press Left, Square, Left, Square, R2, R1, R2, R1.
Hint:
Tips for clean race/lap, lead all laps, or win a challenge race:
1) Use the following setup options: Opponent Type: Same, Catch Up: Off,
Traffic: Off.
2) Select other options/race type as needed to unlock car.
3) Select a slower car. (I use the Lotus Elise.)
4) Select an easy track that you are very familiar with. (I use the National Forest with every shortcut except through the water next to
the bridge.)
If you use the information above, for example, you should only have to slow down next to the lumber mill and just before the bridge after the last turn.
(supplied by: anomynous)