Back Track

200 health
Press Select, then enter L, Right, B, L, R, left. Press A to get the password screen, then enter "HEA".
(Thanks to zombeedude@hotmail.com)

All keys
Press Select, then enter L, Right, B, L, R, left. Press A to get the password screen, then enter "KEY".
(Thanks to zombeedude@hotmail.com)

All weapons
Press Select, then enter L, Right, B, L, R, Left. Press A to get the password screen, then enter "WEAP".
(Thanks to zombeedude@hotmail.com)

Armor
Press Select, then enter L, Right, B, L, R, left. Press A to get the password screen, then enter "ARM".
(Thanks to zombeedude@hotmail.com)

Display coordinates
Press Select, then enter L, Right, B, L, R, Left. Press A to get the password screen, then enter "COOR."
(Thanks to zombeedude@hotmail.com)

Display enemies
Press Select, then enter L, Right, B, L, R, Left. Press A to get the password screen, then enter "MON."
(Thanks to zombeedude@hotmail.com)

Freeze enemies
Press Select, then enter L, Right, B, L, R, Left. Press A to get the password screen, then enter "FRE."
(Thanks to zombeedude@hotmail.com)

Infinite Ammo
Press Select, then enter L, Right, B, L, R, Left. Press A to get the password screen, then enter "AMMO."
(Thanks to zombeedude@hotmail.com)

Invincibility
Press Select, then enter L, Right, B, L, R, left. Press A to get the password screen, then enter "GOD".
(Thanks to zombeedude@hotmail.com)