Evil things

[The Saucepan Man]

...I think....Don't take my word for it...

Indeed, Kransha, since we have no definitive indication as to whether or not most of the beings and creatures that you have identified were of the Maiar.

Ungoliant may have been a Maia, but we cannot tell for sure from the brief description. All we really know is that, according to Elf legend, she crept into Arda from the darkness outside (I don't have my books handy, so I can't give the exact quote).

Dragons are said to have been created by Morgoth, but they may have been inhabited by Maia spirits, since Morgoth (as with all the Valar) could not create sentient life himself. Much the same, I should imagine, goes for Vampires and Werewolves.

I would doubt, however that Watchers or Fell Beasts were Maiar. They seem far more like beasts and, as such, are more likely to have been created and/or corrupted by Morgoth. And as for the great Spiders, even if Ungoliant was a Maia, I very much doubt that her Arda-born offspring would have been.

The only Maia that we can say for sure were persuaded by Morgoth to his cause are, I think, Sauron and the Balrogs. Of the Balrogs, only Gothmog was named, although there are others individually identified (Durin's Bane and the Balrog which Glorfindel (of Gondolin) fought).