I could have put any of George Romero's classic zombie tales in this post. Night of the Living Dead
warped my mind as teenager when I first saw it and is single handily started the zombie genre as we know it today . Day of the Dead was a film that I gained a lot more respect and love for upon my second viewing about two years ago (the first time was the early 90's) as it revealed a whole new layer of how the zombies were evolving. But it was the instant classic Dawn of the Dead that I always felt was the best of the them. Every scene in the movie kicks ass. Plus you gotta love rough ass bikers battling the undead. With all the underlying themes running throughout the movie, it seems Romero had a lot to say about the state of America at the time. And if you dont want to think too heavily about it, just set back and enjoy the Tom Savini special effects.
Does a horror movie get much better than this one? Not for my money. It's right there at the top.