New Background: 
Once you beat the game with Jill or Chris a new background appears on the main 
menu.

New Costume:
When you beat the game with Jill or Chris you get a key. Play "Once Again" and 
go to the room with the large mirror on the 2nd floor of the mansion. The key
is for the door on the other side of the room. Go through it and walk to the 
end of the clothes rack and you can put on the outfit there. Theres another one
if you beat it a 2nd time.

Samurai Edge:
After you beat the game with Jill or Chris you will start with the Samurai Edge.

Rocket Launcher with infinite ammo:
After you beat the game with Jill or Chris you will start with the Rocket 
Launcher and infinite ammo.

Invisible Enemy:
After you beat the game with Jill or Chris you will unlock the Invisible Enemy 
option. All enemies will are transparent.

One Dangerous Zombie:
After you beat the game with Jill or Chris you will unlock the One Dangerous 
Zombie option. You will be followed by a zombie who if you kill you immediately 
die.

Special Features:
Beat the game in "Invisible Enemy" mode in less than five hours to unlock 
a "Special Features" option. 

Grenade Launcher Cheat:
You must have the grenade launcher and two types of ammo, including incendiary
rounds. Put all your items in an item box. Place the Grenade Launcher in the 
upper-left item slot. Place Incendiary Rounds in the upper-right item slot. 
Close the box and open your inventory. Equip the Grenade Launcher, then open
the box and select the incendiary round, the press the A button twice. Then 
move the cursor to the incendiary rounds inside the box and press A twice 
again. This should give you huge amounts of incendiary rounds.