I did some game hacking just for fun after the maps were finished. First I went to the passwords screen and figured out what the alphanumeric digits were. Then I loaded the ROM into a hex editor and searched for the passwords that Hugbot posted earlier. I found these passwords in the ROM easily enough, and when I copied all the nearby data and translated it from hex back to the alphanumeric digits I found several more passwords that the game doesn't normally hand out.
These aren't even on GameFAQs yet!
Play_W_Two - Start on world 2, one player mode
Play_W_Three - Start on world 3, one player mode
Play_W_Four - Start on world 4, one player mode
Play_W_Five - Start on world 5, one player mode
Play_W_Six - Start on world 6, one player mode
Final_Battle - Start 2 player mode, and both players have trophies in every world except world 1
Name_Roll - View the credits
Nine_Nine_Credits - Start 1 player mode with 99 credits
LANG - Activate "special" difficulty
DATA_EAST_CORP - Plays a sound clip. I couldn't hear it well enough to understand.
SHIRAIWA_HANAKUROI - I can't tell wtf this does. It IS a valid password though.