The Walking Dead is indeed awesome. Don't miss it. There's 5 trade paperback collections out now, so luckily you don't have to go tracking down single issues. I believe the comic's release has been in a bit of a slump due to Robert Kirkman working on other projects so the trades have caught up to the single issue releases. It may be a while before we see volume 6, sadly.
For books, you may also want to look into Book of the Dead - The Complete History of Zombie Cinema by Jamie Russell. I haven't read my copy yet, so I can't comment on it too much, but I've flipped though it and it contains a ton of information. It seems to cover all phases of zombie movies and even has a complete (or close to, who knows...) zombie filmography with descriptions for every movie. There's also lot of excellent photos and even a bunch of colour pages as well with some full page movie poster art. Very nice.
I haven't ready my copy of World War Z yet either. I'm planning on reading that when I finish up the book I'm currently on.