The book is already perfect in every way but…
Old Man and the Sea Monster
or, if we’re talking strictly zombies: Old Man and the Sea of Zombies
A Tale of Two Zombies - It was the best of times, it was the BRAAAAAAAAAINS!
I suppose that would be the sequel to Twenty Thousand Zombies Under the Sea, right?
The Zombie Manifesto? Arguably, Marx’s greatest work. Equal brains for all…
… to eat!
Zombie Dick - with Captain Ahab hunting the great zombie whale that ate his leg.
Lord of the Flies - Piggy rises up to slay his tormentors.
I’m not sure the story of The Brothers Karamazombie would change all that much, but Decomposerone would probably be a bit of a drag to read.
The Bible; after the third day Jesus rises from the dead and performs the miracle of loaves and brains.
The Lord of the Ringswould works with zombie orc armies.
The Stand : Just when you think things can’t get any worse . . . it turns out that the Captain Trips superflu had a little after death side effect. Billions of zombies . . .
Moby Dick! Who wouldn’t want to see zombie Ahab take another shot at the white whale?
Zombies would hugely improve Ulysses. A few zombie bloodbaths and it would become a hell of a lot more readable.
After the Greek army destroys Troy, the gods take pity on the slain…and bring them back.
Stephen King already wrote that book. He called it Cell. 
On the Road would lend itself pretty well to a zombie apocalypse scenario. Sal Paradise and Dean Moriarty, two rebels against square, button-down society (and undead brain-eaters) take to the open roads of America, to discover the totality of existence…and fend off hordes of rampaging mindless flesh-eaters.
Well, it’s not the entire book–they cut out and changed huge parts to make it shorter in addition to zombifying it.
The best part is that it has discussion questions at the end.
I appreciate you clarifying that for me. I was going by what the description on the thinkgeek website said.
I haven’t read the book (yet), but now I really, really want to.
Max Brooks’ World Wa–uh, wait a minute…
The best parts are the passages of Zombie Stephen Dedalus’ interior monologue narrated in stream of consciousness style:
brains brains brains BRAINS Brains Brains BRAINS brains brains BRAINS BRAINS BRAINS brains brains Brains Brains brains
Brains Brains Brains
Brains brains brains Brains BRAINS Brains
brains?
brains brains brains brains brains brains brains brains brains brains
BRAINS!!!
Adventures of Zombie-Fearie Finn
Oh think how much more palatable (ha!) Atlas Shrugged and The Fountainhead would be with zombies! Atlas Munched.
Seriously I saw this book at the bookstore a week or so ago and laughed so hard I thought I’d embarrass my teenage daughter. She, however, thinks it’s hysterical too, and joined me.
The Age of Innocence? All that restraint and then … suck out their brains!
I can also see a delectable zombified version of A Clockwork Orange. Rape, pillage, murder … EAT!!
Since the OP mentioned not-so-classic novels, how about Twilight?
“Oooo, cool! His brains are sparkly too!”
- OM NOM NOM NOM NOM *
As Gregor Samsa awoke one morning from uneasy dreams he found himself transformed in his bed into a monstrous, brain-eating zombie.
The bible. Change all begat to ate pronounced at.
Matthew 1:2 Abraham begat Isaac; and Isaac begat Jacob; and Jacob begat Judas and his brethren; 1:3 And Judas begat Phares and Zara of Thamar; and Phares begat Esrom; and Esrom begat Aram; 1:4 And Aram begat Aminadab; and Aminadab begat Naasson; and Naasson begat Salmon; 1:5 And Salmon begat Booz of Rachab; and Booz begat Obed of Ruth; and Obed begat Jesse; 1:6 And Jesse begat David the king; and David the king begat Solomon of her that had been the wife of Urias; 1:7 And Solomon begat Roboam; and Roboam begat Abia; and Abia begat Asa; 1:8 And Asa begat Josaphat; and Josaphat begat Joram; and Joram begat Ozias; 1:9 And Ozias begat Joatham; and Joatham begat Achaz; and Achaz begat Ezekias; 1:10 And Ezekias begat Manasses; and Manasses begat Amon; and Amon begat Josias; 1:11 And Josias begat Jechonias and his brethren, about the time they were carried away to Babylon: 1:12 And after they were brought to Babylon, Jechonias begat Salathiel; and Salathiel begat Zorobabel; 1:13 And Zorobabel begat Abiud; and Abiud begat Eliakim; and Eliakim begat Azor; 1:14 And Azor begat Sadoc; and Sadoc begat Achim; and Achim begat Eliud; 1:15 And Eliud begat Eleazar; and Eleazar begat Matthan; and Matthan begat Jacob; 1:16 And Jacob begat Joseph the husband of Mary, of whom was born Jesus, who is called Christ.