World War Z is written by Max Brooks. The book is written as a series of recollections provided by interviewing survivors of the zombie war. The narrator is from a UN postwar commission trying to get the stories of the war before these people fade away. The book tracks the progress of the infection from beginning to end, providing a lot of entertaining moments as well as tense ones. I am a huge fan of anything with zombies and this is a very intelligent zombie book. The author did a lot of homework in order to keep everything but the zombies themselves absolutely real. As was the case with Romero's movies, there is also political and social commentary parsed in with the story lines.
The author has also written The Zombie Survival Guide. Paramount Pictures is now in production of a movie based on World War Z, due in 2012. Read this book, even if you don't like zombies the survivors stories are very compelling.