The series has a sprawling bestiary, honestly. Dark-Hunters themselves are the obvious start—former humans who sold their souls to Artemis for vengeance and now hunt Daimons. Those Daimons are soul-sucking Apollites cursed by Apollo to die at twenty-seven. Then you've got the Were-Hunters, which is Sherrilyn Kenyon's huge umbrella term for animal-shifters. They're divided into clans: Arcadians (born human, turn animal) and Katagaria (born animal, turn human). That covers everything from werewolves and werebears to werehawks.
It gets weirder from there. Dream-Hunters are beings of the Skotos who can enter dreams, and some, like Arik, get tangled in the human world. There are also gods from multiple pantheons walking around, like the Greek Artemis and Apollo, or the Celtic Morrigan. Demons, vampires that are separate from Daimons, hellhounds, chthonians... the list is massive. I think the most fun ones are the oddball creatures, like the gallu demons or the Charontes, who are these monstrous, loyal fighters. It's less a clean list and more a massive, messy mythological crossover event that's been running for twenty-plus books.