In doing some research on Michael Moorcock for this article, I stumbled across a piece on Something Awful about the original version of the Deities & Demigods book for first edition AD&D. And I don't mean "original" as in "first edition," I mean "original" as in "they got sued and stopped making this version."
The book aimed to provide game masters with ready-made pantheons of gods and goddesses, complete with stats. The original idea was to include both real-world mythologies and those of several popular fantasy authors, but in the end the only one of the latter to stay in was the Nehwon Mythos of Fritz Leiber. Gygax & Co. also included, apparently illegally, the Cthulhu Mythos of H.P. Lovecraft and the Melnibonean Mythos of Michael Moorcock, both of which were removed from subsequent printings. Interestingly, it was NOT because they printed the Lovecraft and Moorcock stuff without authorization that these were removed; in fact, an agreement was reached that would have allowed them to do it. But by that time, both Lovecraft and Moorcock's work were the subjects of games by non-TSR companies, and TSR didn't want to popularize anything done by one of their competitors.
This article is overlong for anyone who isn't truly interested, but I thought it was funny. Unfortunately, when it comes to the missing material, they only touch on the H.P. Lovecraft stuff.
For what it's worth, I have always searched for a copy of that original Deities & Demigods. The first one I bought, in 5th Grade or so, was already neutered. I'm pretty sure the only person I've ever met in real life (as opposed to online) who had that book was this badass drummer, and he would not part with it for $50 even when he was flat broke once back in the day...
I also always wondered why, since all of the world's non-Western major religions were included in the book, why they didn't include major Western religions. I'm sure this was a political choice. Then again, I'm not sure how to incorporate Jesus into an RPG. I can see the text of the "Jesus Christ" entry now...."Christ will NOT strike with his fists for 3-30 points of damage." Heh.