anyone have an actual number?

Well there's..
1. Ash Creatures
2. Wildlife/Animals/Creatures (everything from Kwama to Goblins)
3. Daedra
4. Dwemer machines
5. Undead & Vampires (vamps are NPCs)
6. Fabricants (tribunal only)

http://www.uesp.net/wiki/Morrowind:Monsters

Don't forget that there are plenty of enemies of the "playable race" types as well - Humans, Orcs, Argonians, Khajjit, Dunmer, Altmer, Bosmer.

My worst enemy was poison.

I'd classify as a subcategory to Wildlife -- if not a completely separate category unto itself -- Cliff Racers. Annoying [censored]ers.

Many of the creatures in MW included Diseased and Blighted versions, which used the same models, but had different stats.

You can probably look at the Enchanting sticky to find the list of soul values for all "creatures" in the game. That should be a very thorough list, as it even includes Vivec, etc. I'm not going to sit and count them, though.

Don't forget the CTD