Invasion From Beyond Codes -

Level select:
Press L1, R1, L2, R2, Triangle, X, Circle, Square(2), Circle, X, Triangle at the "Press Start" screen. Return to the "Start Mission" screen to select any level in the game.

All ships, weapons, and upgrades:
Press L1, R1, L2, R2, Up, Down, Right, Left(2), Right, Down, Up at the "Press Start" screen.