Yuan-Ti cults across the planes

How about the Singing Serpents (as Lillendi value music and art).

One awesome, awesome resource i got as an x-mas present one year is the "Dictionary of Ancient Deities" by Patricia Turner & Charles Russell Coulter from Oxford University Press (1997). I'm not going to peruse the whole thing for you, 'cause the index lists no less than 97 references to mythological serpents! I highly recomend this exaustive delve into worldwide folklore to EVERYONE!

oh.....ok....i'll give you three you've (probably) never heard of

Ophiomorphus (Gnostic) - Creator serpent god, son of Ialdabaoth. Creator of the spirits known as the Archons.

Ndengei (Fiji Islands) - Creator. Divine serpent god with stone flesh who hatched mortals from a bird's egg. Ndengei hathed two eggs, from which came a male and a female, the ancestors of the human race. He is also the god of the underworld and judge of the dead. The way to him is barred by a giant with an axe. Whenever Ndengei turns over, earthquakes are created.

Sesha (Brahmanic, Hindu) - Sesha, the world serpent, provides the couch on which Vishnu rests over the primal sea. He is depicted with a thousand heads, dressed in purple, holding a plow and pestle. Sesha was given his name by Brahma, and it means "Eternal". He symbolizes time. At the end of each kalpa (1000 ages), he destroys the world with fire. He is one of the Naga kings who rule in Patala, the underworld.

....these are of course highly edited snippits from the book. The hindu deities have especially long-winded histories, but the book includes (but is not limited to) Norse, Aztec, Maian, Babalonian, African, Persian, Polynesian, Greek, Egyptian, American Indian, Aborigine, etc., etc., etc! 525 pages of VERY SMALL TYPE. Again, any- and everyone should get this book, if for no other reason than to look up the REAL origin of Demogorgon.

There are at least two other lesser CE yuan-ti religious factions who follow powerful and rather archaic Abyssal entities. Sch'theraqpasstt the Serpent Reborn, a primitive uncategorized Demon Lord attributed as the original creator of the Yuan-ti, since fallen to insanity after a failed bid to merge with its own Abyssal Layer. Since its layer is a telepathic dreamscape called the Mind of Evil, I have always considered its cultists to exemplify the psionic aspects of the race. Its avatar is a giant winged serpent.

The Vanguard of Sertrous (3.5 ed. Elder Evils) worship a fallen Obyrith Lord now returning to power. Sertrous embodies the serpent in its aspect as a slanderous deceiver that tarnishes the faith of the pure through heresy, and his form and original portfolio reflect a focus on crawling vermin.