These are just off the top of my head:
Aboleth
Ankheg
Angel (essentially a "class" for good-aligned outsiders)
Animals (badger, weasel, horses, camel, tiger, lion, brown and grizzly bears, etc.)
Ape, Carnivorous
Basilisk
Behemoth
Behir
Beholder
Bird, Riding
Bullette
Catfolk*
Chimera
Demon (essentially a "class" for bizarre weirdness console RPG demons)
Devil (essentially a "class" for classically styled medievalesque demons)
Dinosaurs (key types like the T-Rex and the raptors)
Dragons (all the iconic types)
Draconians
Dwarf*
Elementals (including Positive and Negative elementals, the latter replacing nightxers)
Elf*
Elf, Drow*
Ettin
Fey (a "class" for fey creatures from friendly little faeries to Gentleman With the Thistledown Hair low-epic menaces)
Genies (all four types)
Ghoul
Giants (all the iconic types)
Giff*
Gnome*
Goblin*
Halfling*
Hobgoblin*
Human*
Hydra
Kobold*
Lizardfolk*
Mascot (a "class" for pet monsters, moogles and other 'cute magical critters)
Mind Flayer
Mummy
Neogi
Ogre
Ooze (a couple of types)
Orc*
Purple Worm
Rakshasa
Ratfolk*
Rhemorhaz
Roc
Rust Monster (the Mearls version)
Scorpion, Giant (various sizes)
Scro
Shambling Mound
Spider, Giant (various sizes)
Thri-Kreen*
Titan
Treant
Troll
Vampire
Werewolf (and other lycanthropes)
Wraith (essentially a class for incorporeal undead)
Zombie (essentially a class for corporeal undead, ala Magic the Gathering's sentient zombies)
* Those marked with an asterix I would rather see in the PHB.