John C. Wright wrote an interesting essay for SFSignal on religion in science fiction/fantasy works. I thought there was more substance to what he wrote than this thing I saw a few weeks back. I have read and enjoyed many of the books Wright referenced in his essay, so I think I appreciated it all the more.
However, two of my favorite authors didn't get a mention. The first, Jerry Pournelle may not have got a mention because he doesn't write any of the kind of stories that Wright primarily is talking about. However, Pournelle has a much more accurate take on religion than most scifi/fantasy writers, and that is one of the reasons I like him. Religion can often be a real factor in his stories, and being historically minded, Pournelle usually just uses real religions. One of the first books of his I ever read, King David's Spaceship, was set in a future history that Pournelle and Niven invented, and 4000 years in the future, there were still Christians and Muslims acting much as they do now. In fact, the Catholic Church is still there, having outlasted two space empires that went through civilizational cycles ala Spengler.
Tim Powers probably just breaks the mold, telling stories that often involve the mythical pantheons typical of low fantasy, but with the numinous background of high fantasy. He and Neil Gaiman are sometimes blamed for the fact that we call it scifi/fantasy instead of separating the two.
Wright also mentions Clarke's Childhood's End, which is a book I have never read, but I am nonetheless familiar with due to the nefarious influence of John Reilly. Childhood's End is a millennial story, so it rates a mention in any discussion of the millennium in fiction. Most Gnostic parables of the sort Wright mentions are millennial, but Childhood's End is better than most, and deservedly more famous.