Well as far as any possible Captains go,
Sauron,
Saruman and the
Nazgûl can be ruled out because latter two were killed and the former was diminished into a pitiful little thing.
But I suppose the
Orcs had great chieftains among them, who could have at least attempted uniting the dazzled
Glamhoth.. But as was stated in the RotK, chapter "Mount Doom" I think, the Orcs became sort of paralyzed when
the Ring was destroyed; it's almost as if they didn't actually want to fight, but that they were bound to Sauron's will by the very existence of the Ring. (Ok, ok, I won't start a debate about
Orcish free will..)

But I think you are wrong, Celebthôl, in saying that
Aragorn's army was 'minute' in any way: I don't remeber/know the figures, but all the remaining soldiers of
Gondor, the remaining Dúnedain and the
Rohirrim (who were, after all, allies of Gondor) must have made up an amazingly large armed force! And the Orcs would by now be almost leaderless, as was stated, so they would have little or no organization or tactics.