One - the Balrog
MERP has a list of playable races, so I'll write that down with a brief description. I was actually looking through them to see about any dictionaries/similar. Only found Elvish so far.
Dwarf
Umli - Essentially Half-Dwarves; with Men
Noldo - The "High" Elves
Sindar - The "Grey" Elves
Silvan Elves - The "Wood" Elves
Half-Elves
Hobbits
Men - There are quite a lot of sub-races of men (Duneadain, Rohirrim, Gondorian, etc.)
Common Orc - That's what the book says
Uruk-Hai
Half-Orc
Wild Trolls
Olog-Hai - Essentially Uruk-Trolls
Probably doesn't really help that much, I'll have a look at some creatures...
Balrog, Crebain (the "crows"), Dragons, Dumbledores (giant poisonous wasps found in Hobbit tales), Fell Beasts, Flies of Mordor, Giants, Mumakil
Not much else apart from your standard fantasy creatures and some weirdly named ones I haven't heard of.
Tom is a spirit, as is Goldberry. But there is a debate over
what kind of spirits. OH, can't forget Barrow-Wights!