BLACK UNLOCKABLES
Silver Weapons
Finish the game under normal or hard difficultys. All guns will now be silver and have unlimited ammunition. REMEMBER: The silver weapons will only be available for the difficulty setting you have completed and any lower difficulty settings. This does not include the Black Ops difficulty setting. You will always have silver weapons on that setting.
Black Ops difficulty setting
Finish the game on the hard difficulty setting.
M16A2
Finish the game under the Black Ops difficulty setting to unlock the M16A2 (M16 with grenade launcher) for use on any difficulty setting.