Originally Posted by Kelb_Panthera
If you're looking for originality in D&D you're not going to have a whole lot of luck except with aberations.
Almost every creature of any other type has its origins in some mythological body or other. Drow for instance, hail from norse mythology.
Even aberations are generally a nod toward the works of H.P. Lovercraft and his circle of author-friends, though none of the actual creatures of the type seem to be direct ports from that mythos.
Well, yeah, but as I wrote in the OP, I'm not looking for stuff that has no precedent in anything that came before. For example, as far as I can tell from quick googling after later poster's post, while Drow's source is in Shetland folklore and Norse mythology, D&D has took those two influences, mashed them into a ball and ran with it so far that it would be hard to pinpoint them if not for the name (and in fact there are many more entries in Monster Manuals that resemble those mythological influences much more closely). Unlike, say, Kenku, which aren't very far from Tengu (unless there's some spiffy sourcebook with an in-depth look at Kenku that I haven't heard about).
Also, I remembered another one that qualifies quite well - the Sahuagin. Another one could be Kuo-Toa, but they seem to have moved towards being indistinguishable from Deep Ones during the history of the game.
In fact, pursuing this line of thought I've remembered about the list of WotC's "Product Identity" monsters and that's
and umber hulks and carrion crawlers haven't been mentioned here (and are quite fun).