Well, I'm planning a zombie survival adventure for one of my campaigns as well. However...
I was going to go with the curse route--specifically, the dying curse route. I was going to have the event be localized to one area (an island, specifically--I didn't want this to spread to the mainland and become the dominant campaign theme), as a final defiant spell cast by a dying opponent.
I was considering making a ghoul/zombie hybrid: cannibalistic, diseased bite, relatively mindless, slow & shambling in movement, deadly in a mob. Intended to have them be 1 Hit Die creatures, & didn't want to use a template (I wasn't going to have any extraordinary non-humanoid zombies at all, so a generic monster for use would work great).
I also intended to use this for a low-level (1st-5th) adventure--at a point where the PCs are tough enough to possibly survive, but not to where this would be a cakewalk for them.
As it is, the zombie survival adventure would directly follow another adventure, inspired by The Texas Chainsaw Massacre and other outcast cannibal clan-themed tales/movies. A inbred family of mongrelfolk would be the culprits. One of them would take Leatherface's role (complete with a mask made from faces, and a serrated greatsword of wounding [as a chainsaw stand-in]), another would be the decrepid patriarch, another would be the frantic lunatic (ala Chop Top/Hitchhiker), another would be the responsible/abusive eldest brother/leader (ala Sherriff Hoyt/The Cook), etc. One of the family (maybe the lunatic, maybe the partriarch--didn't decide who) would be a necromancer (either a dread necromancer from Heroes of Horror, or a multiclassed cleric of death/necromancer wizard). This necromancer would animate the skeletons of their victims & send them out as "hunting parties" (along with a member or two of the family); and it would be this character who'd cast the dying curse of the cannibalistic undead (animating the corpses of the slain family members, as well as afflicting the recent dead of a nearby friendly village).
The PCs would have to escape the island (I intended for it not to be feasible for the PCs to wipe out all of the undead), having to fight off the undead versions of villagers and friends who the PCs met and helped previously (in order to make it a bit more heart-wrenching on the PCs, and to make the villains that much more vile).
As it is, I'm reading over the recommendations, too.