Day of the Dead's all right. I dunno, not exactly a favorite of mine.
I did forget to name drop Zombie (a.k.a. Zombi 2, the unofficial sequel to Dawn of the Dead/Zombi; or Zombie Flesh Eaters if you're a wacky Brit). Not my favorite of Fulci's though it's his most popular, but it is a really good movie. Zombie Holocaust—a.k.a. Dr. Butcher, M.D. (Medical Deviate)—is a nice rip-off, heh.
Zombi 3 (Zombie Flesh Eaters 2) is also a flick worth seeing just 'cos of how batty it is. You'll have never seen the variety of zombies featured here—normal slow zombies, super-fast machete-wielding zombies, underwater zombies, and even a zombie head that flies. It's not a good movie by any means, but it's entertaining.