Depends on the kind of zombies we're talking about here.
If they're the generic, slow, peon zombie with no real mental faculties, then pretty much any Pokemon with a decent mount of power can suffice. Any form of typical dismemberment and maiming will generally suffice. Remember, "removing the head or destroying the brain".
Now, if they're your "horde" zombies that tend to gather in large groups, something with wide-spread carnage will be in order. Flight is always a plus here. Pokemon like Charizard and Moltres (flight and Flamethrower) would be great to take out large groups and still make your getaway. If you're surrounded, usually escaping through the ground (via Dig) or by aerial means is often preferrable. So, if this were the case of zombie, I would probably use either a tunneling Pokemon like Excadrill or Dugtrio, or something that could fly and cause wide-spread destruction like Charizard or Moltres. On the other hand, if I were on the outside of a group, moves like Surf and Muddy Water would sincerely come in handy, as they would push the horde of zombies away from you. And, in a last-ditch scenario, you'd probably want to have an Abra on-hand so you could use Teleport and get your but outta there!
However, if they're your agile "run-fast, jump-high" zombie, you want something equally fast. Electrode would be a good one to have, as it could easily catch the zombie, then Self-Destruct and save you (destroying the zombie in the process). Ninjask would also be a good one for flying up and slicing the head off (it IS the second fastest Pokemon ever made). Aerodactyl would be an excellent choice given his rock-hard body (which makes him rather resistant to bites); but also since he can take out large groups with Rock Slide, or a single one with an aerial attack, and since he can fly.
On the other hand, if you're up against your "brute-force" tank zombie, you want something a little more durable. Not something with fleshy Fighting-type that'll just get bitten and zombify. You want something like a steel-plated Aggron, or a rock-bodied Golem! Something that can take a hit and shirk it off like it was nothing. Other options include Magnezone, since he would also be able to strike at range using electrical attacks (which can also paralyze the zombie).
If your opponents are the One Piece "smart" zombie that is fully cognitive you don't have to worry about bites since they're not "real" zombies. So, with that in mind, fighting-types would be an excellent choice to combat these guys, since they tend to be chickens. Unless you're dealing with something like Oz, then you want a Pokemon capable of some massive damage. Volcarona, Darmanitan, and Chandelure would be good choices (as all One Piece zombies hate fire).
Now, if your zombies are the "Bleach Hollow" zombie, you're in for a fight. Again, bites won't be such a problem but you never know what kind of abilities they're gonna have, so you'd really have to play it by ear on this one. Especially if they've become Arrancar.
Of course, if your opponents are of the "Warcraft" variety, and have not only intelligence and sentience, but a nasty little plague called "Blight", you MIGHT want to be using Poison-types or Steel-types. They can be defeated by pretty much any typical method, but their plague is a pretty nasty creature, so do watch out.
Finally, if you're dealing with the other form of "unliving" like Vampires (use Wood Hammer), Ghosts (use Dark-types), or something of the sort, you're really just going to have to play it by ear.
So, it really depends on what kind of zombie you're up against.