Chelsea Quinn Yarbro "False dawn"
Also, if you can struggle through the sheer length of it (and the massive weight of the book), "Ash" by Mary Gentle is a fantastic read that falls into the category, although for most of the book it doesn't feel like it, being more a historical epic (but gentle is a historian anyway, and her medieval realism is superb). In fact, Many of Mary Gentle's works have an End of the World flavour - the "Orthe" dualology "Golden Witchbreed" and "Ancient Light", and the later Valentine White Crow books, especially "Left to his own devices". Gentle is one of my favourite writers.
For a different take, look at books by Sheri S. Tepper. Often written from a highly feminist/conservationist angle, but very well done. You might try "Beauty", "The gate to women's country" (uncomfortable reading for a man), and "Gibbon's Decline and Fall".
Finally, Elizabeth Hand "Winterlong" and the sequel, "Aestival tide" are like nothing else you will ever have read, but are post apocalyptic. Not an easy read, but very rewarding.