Nothing we know of
There are rather few mentions of Mount Doom. A few of those, to my knowledge, mention the forging of objects there, but always the Ruling Ring:
There above the valley of Gorgoroth was built his fortress vast and
strong, Barad-dûr, the Dark Tower; and there was a fiery mountain in
that land that the Elves named Orodruin. Indeed for that reason Sauron
had set there his dwelling long before, for he used the fire that
welled there from the heart of the earth in his sorceries and in his
forging; and in the midst of the Land of Mordor he had fashioned the
Ruling Ring.
—The Silmarillion
Similarly,
‘Alas! yes,’ said Elrond. ‘Isildur took it, as should not have been.
It should have been cast then into Orodruin’s fire nigh at hand where
it was made.
—The Fellowship of the Ring
Note that the first quote makes it clear that Sauron used Mount Doom in many of his other works, but what they are is not mentioned.
Whatever weapons and armor Sauron and his lieutenants wore could have been forged in Orodruin, but there is no proof thereof.
As mentioned by @anaranjada, the battering ram Grond may have been forged in Mount Doom, but again, we don't know:
Fires leaped up. Great engines crawled across the field; and in the
midst was a huge ram, great as a
forest-tree a hundred feet in length, swinging on mighty chains. Long
had it been forging in the dark smithies of Mordor, and its hideous
head, founded of black steel, was shaped in the likeness of a ravening
wolf; on it spells of ruin lay. Grond they named it, in memory of the
Hammer of the Underworld of old.
—The Return of the King
I believe that Sauron's mace is film-only, but even in that case we don't know where it was forged!
