Level Select:
Start a new game and enter !EVAH! as a case sensitive name.

God mode:
Start a new game and enter B4K42 as a case sensitive name. Pause gameplay and you'll find the cheat at the Options screen.

All Bonuses:
Start a new game and enter 105770Y2 as a case sensitive name to unlock all character biographies, vehicle specs, FMV sequences, and concept art.

Thanks to Revolution reader Hellfire!