Film
Night of the Dead
Dawn of the Dead
Day of the Dead (very underrated imo)
28 Days Later
Children of Men
Threads (actually a BBC television play)
Logan's Run
12 Monkeys


TV
Survivors (original 1970's version)

Books
1984 - George Orwell
World War Z - Max Brooks
War of the Worlds - H.G. Wells
I am Legend - Richard Matheson avoid the film version like the plague
The Stand - Stephen King
The Dark Tower series (first book The Gunslinger) - Stephen King
The Handmaid's Tale - Margaret Atwood
The Road - Cormac McCarthy
The Walking Dead - Robert Kirkman (Graphic novels/comics)
V for Vendetta - Alan Moore (Graphic novel)