We are assuming traditional slow, shambling, destroy-the-brain-to-kill-them for this exercise. Fast zombies and smart zombies are another story.
I vote for a .223 or 5.56x45 NATO rifle, probably a bolt-action or single-shot, but an AR-15 clone would offer a higher rate of fire with little accuracy loss and (if maintained...) decent reliability. An AK-74 or other 5.45x39 rifle wouldn't be a bad choice either, due to superior accuracy compared to their 7.62x39 brethren, but you won't be able to raid walmart or dead cops to resupply, and you would have had to already stash hundreds or thousands of surplus rounds beforehand, in which case you're already far more prepared than this discussion will cover I suspect. Sidearm: Whatever floats your boat. If you have to resort to it, you're in trouble already, so go with whatever you're most comfortable using. Melee: You're probably hosed if it comes to this, but a crowbar or framing hammer would probably be the best cheap and effective option.
