Eden Studios' All Flesh Must Be Eaten is the 800 pound zombie gorilla in this space.
Savage Worlds does many things well, but it's pretty much tailor-made to run Zombie Apocalypse.
I'd recommend UKG Publishing's Year of the Zombie, but it doesn't seem to be available anymore.
It used d20 Modern, which I've long considered to be a clunky system, but the atmosphere and writing were top-notch. If you wanted a campaign that kept a serious Walking Dead-style "you could die at any time" feel to it, YotZ was the RPG for you.