Betrayals by Lili St. Crow
Boneshaker by Cherie Priest (ZOMBIE STEAMPUNK! YAR!)
The Boy Who Couldn't Die by William Sleator
The Cell by Stephen King
Chronicles of Nick: Infinity, by Sherrilyn Kenyon
The Enemy by Charles Higson
Feed by Mira Grant
The Forest of Hands and Teeth by Carrie Ryan
The Dead-Tossed Waves (Forest of Hands and Teeth, Book 2) by Carrie Ryan
Gil's All Fright Diner (A. Lee Martinez) has a scene with zombie cows! (but zombies are not the main feature). It is extremely funny.
Hole in the Sky by Pete Hautman
Hollowland by Amanda Hocking
How to be a Zombie by Serena Valentino
How to Draw (and Fight) Zombies by Joe Wight
I Kissed a Zombie and I Liked It by Adam Selzer
Jealousy by Lili St. Crow
Marvel Zombies Series by Robert Kirkman and others
My So-Called Death by Stacey Jay
Never Slow Dance with a Zombie by Ehrich Van Lowe
"Patient Zero" by Jonathan Maberry
Pride and Prejudice and Zombies: The Classic Regency Romance - Now with Ultraviolent Zombie Mayhem! by Jane Austen and Seth Grahame-Smith
So Now You're a Zombie: a handbook for the newly undead - John Austin
SOULLESS by Christopher Golden is YA - and totally awesome!
Strange Angels by Lili St. Crow
The RESIDENT EVILl serialized novels are for both YA and Adults, and feature lots of zombie-like creatures.
ROT & RUIN Series by Jonathan Maberry
My Swordhand is Singing by Marcus Sedgewick (Vampires that act more like zombies)
Undead Much? by Stacey Jay
World War Z: An Oral History of the Zombie War by Max Brooks
You're So Undead to Me by Stacey Jay
Zombie-loan by Momo no Tane (manga series)
Zombie Blondes by Brian James
Zombies: A Record of the Year of Infection by Don Roff and Chris Lane
Zombies Calling by Faith Erin Hicks
Zombies for Zombies: Advice and Etiquette for the Living Dead by David P. Murphy
Zombie Haiku by Ryan Mecum
Zombie Queen of Newbury High by Amanda Ashby
The Zombie Survival Guide: Recorded Attacks by Max Brooks and Ibraim Roberson
Zombies: Encounters with the Hungry Dead by Stephen King, Neil Gaiman, Max Brooks, and S. G. Browne
ZOMBIES VS. UNICORNS edited by Holly Black & Cecil Castelluci is YA

Webistes: has some good titles on their site for the zombie lover.

More Bonus Materials for free ROT & RUIN bonus content:

FIRST NIGHT MEMORIES includes an excerpt from Nix’s Journal and the story of how Tom Imura escaped with Benny on First Night: ****

IN THE LAND OF THE DEAD takes place between ROT & RUIN and DUST & DECAY ****

Adult Books
Z by Michael Thomas Ford
The Forest of Hands and Teeth and The Dead Tossed Waves by Carrie Ryan
Soulless by Christopher Golden
Zombie-loan by Momo no Tane (manga series)
Generation Dead by Daniel Waters
Kiss of Life by Daniel Waters
Passing Strange by Daniel Waters
PRIDE & PREJUDICE & ZOMBIES: DAWN OF THE DREADFULS are Adult, but can be read by teens
DUST by Joan Frances Turner is Adult, but can be read by teens