1,000,000,000 credits for Gran Turismo 3 A-spec:
Finish 50% of the races to get a GT3 saved game with 1,000,000,000 credits.
Unlock All licenses:
Beat the Toyota Pod Event.
Unlock Bonus FMVs:
Finish all of the races to unlock two bonus FMVs.
Unlock Ace mode:
Highlight the Hard difficulty and hold L1 + R1 to change it to Ace.