If you have ArmA II Combined Operations and have not heard about this mod, check it out. It was supposed to a zombie mod but its still in alpha. The online play has gone through the roof with what you can do in the alpha release.
Could be a lot of fun for those of you that play this genre and want to experiment with some free play against other players.
Here are the links:
http://www.dayzmod.com/
ARMA II Combined Operations at Steam:
http://store.steampowered.com/app/2780/