Another vote for Lizardfolk, with a twist.
Make them an uber-lawful stratified caste society, with Poison Dusk and Blackscale Lizardfolk (MM3) each being part of a separate-but-equal pair of castes that each follow very specific roles in their society.
You could even add a touch of Saurial to them, and have the Poison Dusk retain vestigial gliding membranes (being former pteradactyl-like humanoids) and the Blackscales retain some horn-fringes on their heads (being former triceratons). Despite their savage appearance, they would dress in ornate fineries, and the majority of their 'civilians' would have levels in Expert (being exceptional crafters) and Aristrocrat (being also consummate schemers, embroiled in all sorts of eons-old familial and political intrigues). If you want to add 'common' MM Lizardfolk in as a third caste, they could also be more saurian in appearance, perhaps velociraptorish, iguanadon-like or stegasaurian, depending on which way you want to go (or, the common Lizardfolk could represent three or four different subbreeds, statistically identical, but differing in appearance).
Despite their advanced culture and philosophies, they would still decorate themselves in 'savage' fineries, such as cloaks of brightly colored feathers or patterned animal hides, and clattering jewelry made of intricately carved bones and river-polished stones, creating a sense of disconnect in viewers of other races, who might initially see them as primitives, only to be rudely surprised...
To go with a completely different twist, have them appear to be human (albeit albino, perhaps from a millenia living underground), but actually be from that Human sub-race introduced in the Book of Vile Darkness. The plague / disaster that wiped out their world? Yeah, that was deliberate, they decided the easiest way to kill the gods was to kill all of their worshippers. They've poked their heads up and are very, very disappointed to find out that life has returned. Time to dust off the old genocide plans and start again...