Extra lives:
At the title screen press Up, Up, Down, Down, L1, R1, L2, R2, L3, R3.

Picture gallery:
Beat the game twice, or get an A rank the first time through.

Theater:
Beat the game with a B rank.

Lucia:
Beat the game in twenty minutes on easy.

Bill II and Jaguar II:
Get an S on level seven.

Thanks to Revolution readers Paco Escovedo, and Andrew Shoeful!