Let's see...
1) Samus Aran, Metroid series, at full power with all upgrades. Those zombies would be toast, at least in relatively small numbers. However, Samus' precision beam and limited missiles means she is liable to get overwhelmed, so for that reason I'd also like to have...
2) Jorge, Halo: Reach. The machine gun he lugs around with him would tear the hordes to pieces. Also, he's damn tough to kill.
Lastly:
3) Mordin, Mass Effect 2. His medical expertise means we'd probably be safe if we got wounded, and he might even be able to invent a cure for whatever it is causing the mass zombification. Plus he's funny, and can point a gun straight.