The Last Stand is a cool zombie base defense flash game. It was made by Con Artists Productions, and released through Armor Games. It's very much like other base defense games in terms of the basics, but several things distinguish it from others.
Instead of money or whatever to improve your base, you have a certain number of daylight hours each day to distribute between repairing the wall, searching for survivors, and searching for better weapons. More survivors allow you to get more done with your hours, and at night they help you fight off the zombies. Unfortunately, sometimes your survivors don't... well... survive the search parties.
Another distinction is that the graphics and animation are rather good. Many base defense games use very basic graphics, but these actually have a polish on them.
Make sure you click on the diary each day when you're choosing weapons. It adds some flavor to the game.
Also, I just noticed that Last Stand 2 has come out. I'm going to have to play that...