$5,000,000:
Enter chimchim as a case-sensitive name in Career mode.

All drivers:
Enter mitymasta as a case-sensitive name in Career mode.

All tracks:
Enter joeyjoejoe as a case-sensitive name in Career mode.

Arcade style handling:
Enter megedereck as a name in Career mode.

Thanks to Revolution readers Wizza, Erich Schindler and Josh Arnold!