There was a module in Dungeon Magazine a few years ago, Tammeraut's Fate. I am a great advocate of this module, because it did D&D zombie apocalypse, albeit on a very small scale (ie one remote island, as opposed to the entire world), very well. The reason it worked so well was because of time - the characters get to the island, realize that it's been attacked by an army of sea zombies in the night... then the sun goes down.
Despite the high magic inherent in D&D, an overwhelming force, especially against a group low on resources and time, is still scary. Any ol' zombie template will do (since they're all over the place, really), as long as the fear of contagion and massive numbers is there. Zombies are very much a case of presentation over stats (although a good set of stats is very helpful).
Demiurge out.