Is “war day” the book told from the perspective of a guy in new york city right as the war starts? I think I might’ve read it in middle school.
When I was in middle school, we had to read a short story about a primitive hunter wandering through a ruined “city of the gods”. Somehow he gets a vision of the apocalypse and realizes that the “gods” were his own ancestors. It was written before World War II, but my English teacher claimed that it contained a lot of small details that were consistent with the destruction in Hiroshima and Nagasaki. Does anyone out there know this one?
In a similar vein, perhaps Star Man’s Son by Andre Norton. It’s written for “young adults” but it’s a fun read.
Two I’m am deeply ashamed for omitting the first time 'round:
Childhood’s End by Arthur C. Clarke
I Have No Mouth and I Must Scream by Harlan Ellison (and I named two other Ellison stories before this one! What the hell is wrong with me?!) Also made into a kick-ass computer game, or so I am told (never played it myself, but I heard good things)
Woohoo! One of my recommendations isn’t on the list yet!
Telempath, by Spider Robinson. Also, Earth Abides & Emergence.
Another vote for A Canticle For Liebowitz. It’s very fine.
Dangyou, Ethilrist! I just finished re-reading “Telempath” and was about to post it!
“Triffids” is a lot of scary fun. Did anyone here ever see the British TV version? I saw a very tiny portion of it years ago and am wondering if it was a dream…
I have a copy.
I second “I am Legend.” Incredible book. The Omega Man is an incredibly poor adaptatation that drops the most important theme (actually the central message) of the book.
I’d also second “Swan Song” by Robert McCammon. Unusually good for McCammon, who’s pretty hackish. Has one of the creepiest lines in any book I’ve ever read (from one of the villains): “I’m a carpenter. Jesus was a carpenter.”
“A World out of Time,” by Larry Niven isn’t strictly post-apocalyptic (it’s more in the vein of “The Time Machine”), but it is very interesting.
I’ve read most of the books mentioned in this thread, and I give a hearty second to Davy. It, and some associated stories (published, I think, in the collection Still I Persist in Wondering) are wonderful.
Only question - are they still in print?
I agree that Canticle for Leibowitz is good - the sequel, however, I found to be poor. It was finished by someone else after Miller’s death, and, to my surprise, I thought the non-Miller part was the best.
sigh All of my recommendations are already there, so I’ll second/third/whatever The Stand, Swan Song, On the Beach, and The Last Ship.
And here I thought sure I was the only one who read the last one! 
And Scupper, have you read McCammon’s newest, Speaks the Nightbird? It’s very different from Swan Song, but it’s far from “hackish.” In fact, his last three books have all been pretty good. Though I agree that his early work was obviously early. Even he agrees, as he pulled his first four novels from re-printing.
More votes for:
Earth Abides. I think this is exactly what the OP is seeking: a serious examination of how society would react to a catastrophic event (a plague), and the book is regarded as a landmark of the genre.
A Canticle for Liebowitz.
Day of the Triffids. The premise sounds silly, but Wyndham is such a great writer he makes it work.
Usram wrote:
This was also published as No Blade of Grass, but I’m not so sure it fits the OP’s description. It was a little heavy on the gunplay and (as the OP puts it) “testosterone violence fantasies” for my taste. I really liked the cataclysmic premise though: a virus wipes out all grass species (including rice, corn and wheat).
Lucifer’s Hammer also has a lot of gunplay, but it is very well written and thoughtful, and otherwise meets the criteria of the OP. I would recommend it.
I cannot recommend The Purple Cloud, which (IMHO) answers the question, “What if the last man on Earth were a gigantic ass?” The main character was so unlikeable, I couldn’t enjoy the book.