There are other pantheons which have not made it into the AD&D game (or, not to a significant degree). Deities from some of these pantheons have been mentioned on occasion, however. I don’t have sources on most of these pantheons at this time (other than Hittite), but there’s definitely some interesting potentialities among them. Much of my current knowledge is from books on other topics that just tangentially touch on these pantheons. Of these, the Hittite pantheon is one I would certainly be working on at some point, while most of the others are far less likely
Slavic Pantheon, an Indo-European faith mostly known from Christian writing:
—Chernobog
—Perun
—Stribog
—Svarog
—Svarozhits
—Veles
Baltic Pantheon, an Indo-European faith mostly known from Christian writing:
—Perkunas
—Velnias
Hittite/Hurrian/Hattian, peoples of Anatolia; the Hittites were Indo-European but much of their faith was drawn or adapted from the earlier, unrelated Hurrians (who may be related to the Urartians) and Hattians, as well as drawn from Mesopotamia:
—Hannahannah
—Kumarbi
—Shaushka
—The Sun Goddess of Arinna
—Tarhunna/Tarhunt
—Teshub
Elamite, the religion of the peoples of the Iranian highlands east of Mesopotamia and the great rival of the Sumerians. Little is known of their pantheon, however.
—Inshushinak
—Kiririsha
—Napirisha
—Humban
—Pienenkir
—Nahhunte
West Semitic/Canaanite/Phoenician mythologies, all closely related to each other, and related to the mythologies of Mesopotamia, these faiths were the people of the Levant and eventually Phoenicia. Many of them are prefixed with Ba’al, which means Lord. Many of the deities entered Christianity as the names of demons.
—Aglibol
—Astarte
—Ba’al Hammon
—Dagon
—Melqart
—Yarhibol
Persian/Zoroastrian, the ancient Persian religions show some close similarities with the ancient Indian pantheon of the Rig Veda, with Zoroastrianism being a direct outgrowth of it.
—Ahura Mazda
—Mithra (popular among Romans, as well)
—Ahriman (Guide to Hell indicates Asmodeus is actually Ahriman)
African Mythologies, detailed in Dragon Magazines #191 and #215; multiple different mythologies are merged into one much as the Celtic pantheon did.
—Ala (Dragon #191)
—Ananse (Dragon #215)
—Antelope Man (Dragon #215)
—Asase Ya (Dragon #215)
—Bumba (Dragon #215)
—Cagn (Dragon #215)
—Chameleon Man (Dragon #215)
—Eshu (Dragon #191)
—Gauna (Dragon #215)
—Khonvum (Dragon #215)
—Leza (Dragon #215)
—Lion Man (Dragon #215)
—Nyame (Dragon #215)
—Obatala (Dragon #191)
—Olokun (Dragon #191)
—Olurun (Dragon #191)
—Orunmilla (Dragon #191)
—Porcupine Man (Dragon #215)
—Shango (Dragon #191)
—So (Dragon #215)
There’s certainly many more pantheons and faiths out there, but I know them even less than these! I’m always up for investigating these other pantheons, however.