God Mode:

During a single player game, press L + R + X (or B) on controller 2 to toggle invincibility and infinite ammo.

AI toggle:

During a single player game, press L + R + A on controller 2 to toggle enemy firing.

Unlock the Speed Board:

Beat the boss on the U.S. track.

Unlock the Trick Board:

Beat the boss on the Japan track.

Unlock the Combat Board:

Beat the boss on the U.K. track.

Turbo Start:

Hold R when the word "Go" appears in the beginning countdown.