The Last Stand 2

http://www.maxgames.com/play/last-stand-2.html

This is the successor to the thrilling survival flash game "The Last Stand"! Some things have changed, like for example you can select where to search during the day. You can set up traps as well, and shoot at them during the zombie attack at night. Plus, now you can even equip your survivors with weapons.
Sadly there is not sky visible like in the first game, that will show the dawn of a new day. Still, very entertaining and this time you have to last 40 full days!

13 Days in Hell

http://13-days-in-hell.freeonlinegames.com/

Yay, more zombies !
and this time you can head/waist/whatever shoot them :D
Having to buy your ammunition adds some additional challenge to the game and rewards a good aim and cool hand even in the most wicked situations more then any points given ^^
And it saves your progress, always a big plus.

BOXHEAD: The Zombie Wars

http://www.boxhead.seantcooper.com/Boxhead_TheZombieWars.aspx

Jon Bambo is alone. Ok not that alone,  by his side his trusty pistol, shotgun, turrets and other tools crafted to put those hordes of zombies to pieces.
Nice top down survivel shooter with many, many zombies to kill.
Every few kill multipliers you get upgrades for your guns and your base placements.

So thousends of zkp (zombie kills per minute), a minigun and a nuclear airstrike, what else do we need to be happy ?*

*ok, i heard  someone shout "boobs", maybe in the next version ? :P