Haradrim:

The Men of Harad. Also called Southrons, the Haradrim served Sauron. It was the Men of Harad who used the Mûmak as war-beasts in the War of the Ring.

Hasufel:

The horse Éomer loaned to Aragorn.

Half-Orcs:

Bred by Saruman in Isengard, the Half-Orcs were used as spies and soldiers in his search for the One Ring and his fight with Rohan. They were bred from Men and Orcs. Some were less orc-like than others, and they were the ones usually used for spies such as the one who hid in Bill Ferney's house in Bree.
But there were some others that were horrible: man-high, but with goblin-faces, sallow, leering, squint-eyed. Do you know, they reminded me of that Southerner at Bree; only he was not so obviously orc-like as most of these were. (LOTR.589)

Huan:

Wolfhound of the Valar, Huan went to Middle-Earth with Celegorm. Fated to speak three times before he died, and only to die at the hands of the mightiest of the Werewolves, Huan left Celegorm, with Lúthien, and aided her in freeing Beren from the dungeons of Sauron. Huan died at the hands of Carcharoth, when they finally found him during the hunt.

Huorns:

These are trees that are able to move. In Fangorn Forest, they were cared for by the Ents. It is believed that many of the trees of The Old Forest were also Huorns, given their behavior as Merry said:
They do say the trees do actually move, and can surround strangers and hem them in. In fact long ago they attacked the Hedge: they came and planted themselves right by it, and leaned over it. (LOTR.125)
Treebeard supported this idea when he was asked about it by Merry.

The Lord of the Rings
The Silmarillion
The Unfinished Tales
The Hobbit
The Complete Guide to Middle Earth by Robert Foster