Earn To Die - If you like cars (and already likes games like Carmageddon), then this game is definitely for you, because here you will have the opportunity to drive some vehicles, to upgrade them and even run down some (many) undead. Life could not be better, does not it? And the cool thing is that it already has continued in two parts, in other words, if you like the former can continue to share in the second and finally the third game in this series.
BoxHead - A Halloween Special - If you prefer the classic style, that is, gun in hand, and shot very "runs the zumbizada coming!", Then you'll probably like this game more. In Boxhead, all the characters are well caricatured ("Box Head" is the translation at the foot of Boxhead letter, by the way) and this gives the game a unique air. In it, you will be an agent in a city, doing missions on the type meet the survivors and bring them safely to the place X, needing to eliminate the zombies that are in the way and trying to keep everyone alive - which is not always possible, fact.
Deanimator - this was one of the first zombie games I played online - and I'm concept fan of his ever since. The idea is simple: you are a scientist who accidentally did the dead back to life and now need to prevent them from reaching the city. For this you will have a gun (infinite ammo) and a shotgun (you get ammunition for the same eliminating some zombies). Although you do not move in the game and the only actions available are shooting, reloading or changing weapons, you will find that need a good aim, know the right time to choose each weapon and a little luck. Oh, and death is inevitable, so do not take it personally.
These three games are, for me, some of the classics when it comes to zombie games. If you do not know them, take the opportunity and play a little bit of them right now, I'm sure they will entertain you enough!