This is a sub-page of Half-Life: Opposing Force.
Black Ops Osprey#
The Black Ops were to have their own V-22 Osprey at one point. It was cut, but the model for it is still in the game.
It also has its own model for gibs.

Destroyed Black Ops Osprey#
The Black Ops Osprey also has a "dead" variant that is also unused. It looks the same as the "dead osprey" model that appears throughout the game, but with the Black Ops coloring on it.

Dead Gordon Freeman#
The model deadhaz.mdl contains an unused variant with Gordon's head instead of the generic HEV Suit helmet.
Flash Grenade#
An item model for an unused Flash Grenade can be found in the game's files. The same flash grenade, albeit less detailed, can be found carried by Black Ops assassins.
This and the lack of a first person model could mean that these flash grenades were supposed to be a monster-only weapon used by the Black Ops assassins alongside frag grenades to further hinder the player.
Human Grunts#
Black Commander#

The 8th head for the friendly grunts is unused, but fully defined in the code and can be selected as a possible head choice for grunts in custom maps.
Black Medic#

Much like the regular troops, the medics also have an unused head which is fully defined in the code, and can be used in custom maps.
Singleplayer .357 Magnum Revolver#
While the .357 Magnum Revolver can be found in multiplayer mode, the player can only see its multiplayer version. The single player version (without the laser sight) can't be seen without cheats because it does not appear in the single player campaign.
Suppressed Pistol#
The suppressor for the Pistol is still in the game, but some changes to the weapon's model have made it so that the suppressor floats underneath where the barrel is instead of being attached to it. The "add_silencer" animation is still there as well and has the same problem.