Rogue Survivor is another for the list.
It's a free tile-based rogue game which features barracading, scavenging, shambling zombies etc. The base game has some fantasy elements like skeletons that detract from the zombie theme but there's a great mod which brings it more in-line with zombie canon:
Base game:
http://roguesurvivor.blogspot.co.uk/
Mod:
http://roguesurvivor.proboards.com/index.cgi?board=gmods&action=display&thread=264
That looks really good!

No idea what these missions are all about but it looks ok if your into zombies.
How haven't I come across these before?
