[DGStahler]

Anything that creates an "End of the World as WE Know it" fits my definition of Post-Apocalyptic.

Some of my favorites for "current apocalypses",and this includes zombies, are:
EMP Lodge series, by Grace Hamilton, 6 book series
Zombie Rules series, by David Achord, currently 6 books
Keep your Crowbar Handy series, by S. P. Durnin, currently 4 books

For an apocalypse that happened "long ago" , a couple of my favorites are;
A Canticle for Liebowitz, by Walter M. Miller Jr.
Heiro's Journey and The Unforsaken Heiro, by Sterling Lanier, there i/was supposed to be a third book, but it has never been published.

A more science fiction sort of approach to the post apocalyptic genre is represented well by;
The Safehold series, by David Weber
The Pern series, by Anne McCaffrey, not sure if you would call these science fiction with a fantasy twist or fantasy with a science fiction twist.

All of the above are excellent reads and well worth the effort of tracking them down.

I think you could add the following to this thread as well -

Jack Vance - The Dying Earth series:
The Dying Earth.
The Eyes of the Overworld.
Cugel's Saga.
Rhialto the Marvellous.

Gene Wolfe - The Book of the New Sun:
The Shadow of the Torturer.
The Claw of the Conciliator.
The Sword of the Lictor.
The Citadel of the Autarch.

[fraidycat3]

Highly recommend the classic "Alas Babylon" by Pat Frank.

[AhhhChoo]

Davy - Edgar Pangborn

[Dendra]

Brave New World by Aldous Huxley.
And a second to Wool by Hugh Howey.