Now, here's a game that will cater to the refined tastes of the people who don't really enjoy spending money: Zombie Plague. An excellent and free board game (well, you will be needing a printer; and some ink; dice would come in handy too; other than that it's free) that pits humans vs. zombies, or, to be more precise, fast and well-armed humans vs. slow and defenseless zombies. Great tactical fun.
Zombie Plague Link