I already mentioned Hyperion for Dan Simmons. I think that's the best of all his sci-fi books by far.
Nevil & Pournelle "Lucifer's Hammer"
Another really good one. This one is end of the world by a comet.
A Canticle For Leibowitz.
Good Omens
For another odd take on the Apocalypse, check out Sir Fred Hoyle's October the First Is Too Late, published in 1966.
I consider it post-apocalyptic in a sense of being gone from the Earth long after the apocalypse. It certainly is interesting in the way it looks at the Catholic Church as an "interstellar" institution (I bet they hate this book with a passion).The Hyperion series is most excellent, but I would not at all describe it as being apocalyptic or post-apocalyptic.
Alas Babylon
