Orcs: The most numerous and common enemy in Middle-earth, orcs are brutal, warlike creatures bred by Morgoth. They are fierce fighters, though not particularly intelligent or brave.
Trolls: Large, brutish creatures with immense strength and a love for eating and fighting. They are often encountered in caves and mountains.
Goblins: Smaller, more agile than trolls, goblins are also vicious and cunning fighters. They are often used as scouts or skirmishers.
Wargs: Large, wolf-like creatures that can be ridden by orcs. They are swift and deadly predators.
Uruk-hai: Bred by Saruman, Uruk-hai are a hybrid race of Orc and Man, with greater strength and resilience. They are cunning and ruthless warriors.
Wights: Reanimated corpses that serve the forces of evil. While not technically "monsters" in the same way as the others, they are powerful and fearsome warriors.
Nazgûl: The nine Ringwraiths, servants of Sauron, are powerful beings with immense power and a terrifying presence. They are skilled warriors and masters of fear.
Giant Spiders: While not typically thought of as warriors, the giant spiders of Mirkwood are powerful and deadly creatures that hunt and kill with ease.
Drakes: Powerful, winged dragons that are fierce warriors and deadly opponents. They are rare but powerful creatures.
While these are just a few examples, there are many other creatures in Lord of the Rings that could be considered warrior monsters. The term "warrior monster" can be subjective, depending on your own definition.