All of them?
For gaming purposes, I'm particularly fond however of:
Japanese
Norse (broadly "Northern European")
Yoroba (broadly "East African")
However, in terms of aesthetics such as art and architecture, I very heavily borrow from Hindu and Mayan. I would also say that very fine theological or cosmological distinctions are hard to draw, and because everything is being imported into a completely different theological and cosmological framework anyway, that saying I'm doing even pastiche of any of the above would be a stretch. I think it would be almost impossible to claim any sort of fidelity unless you also have a historical setting.
I think it's almost impossible to play D&D and not have some influence from Greek myths, as the bestiary is chock full of creatures loosely inspired by Greek myth.
In short, I would have a very hard time narrowing it down in practice to three.
UPDATE: Oh yeah, Slavic is good too.