One of the most interesting mythologies to me is that of the peoples of Mesopotamia, chief among them being the peoples of Sumer and Akkad. The Sumerians pioneered writing, and as such their language persisted as a liturgical tongue throughout the region as their religion persisted in the descendants of the region, Assyria and Babylon. One of the strange things in the early D&D material is the splitting of the Sumerian and Babylonian mythoi, which are not truly separate faiths, just temporally separated versions of the same religion. Of course, like all religions that span centuries or millennia, significant divergences occur at various points, especially as cities with their own take on the faith rose and fell; this is the reason the Babylonian and Assyrian versions of the Enuma Elish creation myth place their primary gods Marduk and Assur in the leading roles respectively. As with the Egyptian pantheon, describing different ways of setting up the pantheon would be integral to properly describing the pantheon.
I have a large number of sources for this mythos, but I have misplaced some of them right now, so this list is based on some of my old notes. There are literally thousands of known deities, many of which have little solid information, or are local versions of other gods, or deified concepts of minor locations or things. I’ll just be listing major ones here. There are other culturally related or influenced mythologies that I will mention in a later post, that may be most appropriately integrated into this mythos.