Meso-American and Polynesian cultures, namely the Ancient Mayans and Hawaiians, are underrated in my opinion.
The Mayan culture mirrors Ancient Greece in many ways, both were known for astronomy, astrology, architecture, mathematical systems and art; just the Mayans receive a lot less spotlight in mainstream fiction and media.
I have a few races drawing from Mayan and Hawaiian culture including a black tengu race and "goblins" (actually nothing like goblins, they represent more tarsiers and despite being indigenous are not antagonistic in any way). Sacrificial acts, temples and worshipping of the stars are prominent in their culture and they dwell in rain forests or near volcanic areas and coastlines. Their languages derive from the pictograms used in Mayan culture and words used in the ancient Hawaiian languages.
I feel these two tribal cultures are underused.