I think I'm with the near consensus on the Left 4 Deads. I'd argue they are neck and neck with one another for the top spot, given the setting change, and quite a few game mechanic changes between the two.
I also think 7 Days is a very worthy successor. Much more so that Overkill's Walking Dead, which really dates the article... since the game was so bad, it was pulled from Steam, and basically, everyone involved with the project would rather the world forget it. Quite sad too, since one would have thought a mod of Payday 2 with Robert Kirkman's blessing and oversight would have been capable of being Left 4 Dead at it's own game.
While it's not my cup of tea, Call of Duty's Zombies is probably the reigning champion of the sub genre in terms of notability. Dead Island is quite fun, despite being enormously flawed as a whole.
The Crafting Dead mod for Minecraft is also quite good.