Sound test option:
Kill 1,000 zombies.
Movie test option:
Kill 2,000 zombies.
Kill 100 Bosses.
Unlock Boss Mode (a different way):
Type in D0ntn33dm0n3y in the password screen.
Unlock "View Ending" :
Clear Chalenge Mode (defeat all the bosses on all the tables) to unlock View Ending. You can now watch the ending and credits at any time!