Earth Abides is very good, as are Stephen Baxter's Flood & Ark, lots of great suggestions, you could also try;
Alas Babylon, Pat Frank
Death of Grass, John Christopher,
The Drought, J G Ballard
Far North, Marcell Theoux
A Canticle for Liebowiz, Walter M Miller
Oryx & Crake, Margaret Atwood
A Wrinkle in the Skin, John Christopher
Greybeard, Brian Aldiss
Nod, Adrian Barnes
The Postman, David Brin (super-shit film though)
The Dog Stars, Peter Heller
All apocalyptic/post apocalyptic.
Zombie-wise The Passage & The Twelve by Justin Cronin are very good, & World War Z is brilliant, ones that haven't been mentioned are;
The Return Man, V.M Zito
The Reapers are Angels, Alden Bell
The Forest of Hands & Teeth, Carrie Ryan (there are two sequels, The Dead Tossed Waves & The Dark & Hollow Places)
I, Zombie, Hugh Howey
I could go on, it's one of my favourite sub-genres.