This was brought up in the Walking Dead Season 2 thread, but it deserves its own thread. I recently just got caught up on all the entries/stories, and I have to say that this is the best zombie story I've ever encountered.
It's highly addicting, so don't even start unless you plan on devoting the next few days/weeks reading it. It is still being updated regularly, also, so the story isn't over by a long shot.
EDIT: Goddamn it can a mod please spell check the title to this thread.