World War Z - Great Zombie Apoc
The Road - As mentioned above, is a GREAT story! sure it may be POSSIBLE to take it as religious in undertones, that is how you choose to interpret it... It is worth a read though!
Z for Zachariah - About a sixteen year old girl in a world ravaged by a nuclear holocaust... I thought this book was fairly well done... Rather simply written though.
Dies the Fire - Awesome start to series of books (which I have yet to read the others) about basically the world having a reset button hit, as all tech was pretty much destroyed by an EMP... IT sends the world back to a fuedal state... and it is a GOOD time!
I am Legend - Richard Mathesons short novel is FAAAR better than any of the adaptations EVER made for film... This is a GREAT story, has an edge of fear, and captures the bitter loneliness of Robert Neville brilliantly... I recommend this for fans of horror, post apoc, and just fucking good stories!
The Chrysalids - The Chrysalids is set in the future after a devastating global nuclear war. David, the young hero of the novel, lives in a tight-knit community of religious and genetic fundamentalists, who exist in a state of constant alert for any deviation from what they perceive as the norm of God's creation (description taken from amazon... i havent read this yet, but its on my list)
Well Im sure there is more I will think of later.... Oh The Stand... thats a great one too!
Hope that helps a bit!