My recent explorations into Gamma World (and post-apocalypticism generally) brought to mind Walter M. Miller's 1960 novel, A Canticle for Leibowitz, which I have considered one of my favorites since I first encountered in high school. The novel is an outgrowth of three science fiction novelettes Miller wrote for publication, only two of which ever appeared independently (both in the pages of The Magazine of Science Fiction and Fantasy). It was while working on the third that Miller decided to rework it and the two previous ones to create a single novel consisting of three parts, each of which told a portion of a larger story.
A Canticle for Leibowitz takes place some six centuries after a nuclear holocaust (known as "the Flame Deluge" in the setting) has ended human civilization as we now know it, creating a new dark age. The survivors of this disaster took out their anger not just on the scientists whose weapons had brought it about, but on all learned people, leading to the destruction of much knowledge, including books. What knowledge survives is largely in the hands of the Church, repeating its medieval role as a preserver and copier of ancient texts. All three parts of the novel focus on the Albertian Order of Leibowitz, a group of monks founded by a military engineer who converted to Catholicism and decided to stem the tide of "the Simplification," as the destruction of knowledge was known.
The novel's first part (Fiat Homo) centers on Brother Francis Gerard, a young monk who discovers a ruin in which he finds possible relics associated with Leibowitz, whose cause for canonization is currently under consideration in New Rome. The second part (Fiat Lux) takes place hundreds of years later, after Leibowitz has been declared a saint. Civilization has crawled back up to roughly the level of the Renaissance or early modern period, with technology similarly advanced. Rising nation-states covet the Church's store of knowledge and seek to use it to pursue their own agendas. The third part (Fiat Voluntas Tua) is many more centuries in the future, after humanity has developed nuclear weapons and space travel. Two super-powers are on the brink of war and a new Flame Deluge seems likely, with the Church taking steps to ensure that, once again, all knowledge is not lost in the coming conflagration.
A Canticle for Leibowitz is, as I said, one of my favorite books and made a strong impression on me a a younger man. While far more "realistic" than, say, Gamma World, I've nevertheless imported elements of the novel into most post-apocalyptic RPG campaigns I've run. The world Miller describes, as well as the situations, are very compelling and, above all, very human. His is not a world of black-hatted villains and white-hatted heroes but of people trying to do right according to their own lights, even when "doing right" is often, by some standards, quite evil. It's that complexity that sets A Canticle for Leibowitz head and shoulders above most other post-apocalyptic science fiction of its time (or indeed any other).
Miller himself was an interesting character. He served in the US Army Air Corps during World War II, mostly on bombing missions. One such mission involved the destruction of the Benedictine abbey of Monte Cassino, the mother house of Western monasticism, which the Allies mistakenly believed was being used by the Germans as an ammo dump and staging ground. Interestingly, it was German commanders who, upon learning of the possibility of an attack on Monte Cassino, ordered its treasures to be taken away and put into the custody of the Church so that they might be preserved. Miller was so moved by the destruction of Monte Cassino that he eventually converted to Catholicism and spent much of his life haunted by his hand in it. A Canticle for Leibowitz is clearly inspired by his experiences in World War II.