Some other (Scarred Lands-based ideas )
Race of crocodile warriors with a ruling priest caste. Based on Paragorn Crocodiles from CC-1 - viscious and tough physically, with a spell casting elite. Curse them - for hubris, failing their god, challenging the wrong god etc etc - to make them undying (Curst template from Monsters of Faerun might be a nice combo).
Thulkans (from CC-2) - an undying creator race that still hangs onto its by now pointless destiny, creating superior weaponry, arms and tools and still preparing for a war that has already happened. Have them try to enslave/entice the human realms in the surrounding lands to serve their (long-forgotten ?) purpose in exchange for superior weaponry with with each could gain supremacy over its neighbours
The High Gorgon (CC-2) mentioned above would really fit the part - human enough, yet definitely non-human at close examination, frightening if need be ( Are snaky tentacles erupting from the belly bad enough ? ) and reasonable spellcasters to begin with. Originally worshipping a titanic snake entity - defeated at the moment, but the Gorgons are working onits rebirth ? Or simply fulfilling its final plan ? Would suit a Lovecraftian evil entity admirably.....
as sidekicks and servants - Ukrudan Stalkers (CC-1) and Sand Mummies (CC-2) just scream for an adaption into a cursed desert scenario, be it as hired help or as random hazards
and a classsic D&D spin
Thri-Kreen (MM-2) - Insectile, desert adapted race with possible psionic angle ? Close enough to human in heavy robes disguise, utterly alien if outside. Get some nostalgic Dark Sun goodity !
Oohhhh, how about some desert dwelling variant of Spriggan giants (FF) ? Make them less chaotic (life in deserts tends to make you more open to rigid, structured patterns ), more hateful and - oh my - cursed..... Get "Evil Jawa" ! Would give them nice spying capabilities - plus, you might get really mean with their larger "combat" form