Meenlocks? Flail snails? Quillons? Al'mir-aj (I'm quite certain that spelling is totally wrong)? Carbuncles (weren't those the little unicorn rabbits? Nasty sharp pointy teeth?)? Volts?
The flumph, of course, was mentioned by the honorable Felis catus buccaneerius above.
Sadly, the Giant Space Hamster has shown up in ToH I.
Aleax showed up, but not in any of those books.
Did magnesium spirit show up? How about the origninal Water Wierd (not the womanly shaped oracle)? (I swear I've seen the writeups to both -- like the Water Wierd renamed a Drench in some NG module.)
stained glass golem from the 2nd edition monster manual I haven't seen. I thougt that was an awesome monster and was dissapointed when it wasn't in the monster manual I, II, or III.
Also I don't know if the scarecrow golem has been in any yet either