The Walking Dead

By far the best comic about Zombies is The Walking Dead written by Robert Kirkman.
Basically Kirkman has taken the well known Zombie story one step further. Where most movies end with a few survivors The Walking Dead goes on. The survivors are followed on their road to safety, their path of survival between the undead.
The survivors have to find a safe haven, have to trust people they don't know, have to grow their own food etc.
What happens during the story is that not only the undead but the survivors themselves start to become their own enemy. People losing their mind, being unable to cope with the situation.
Kirkman is able to write a story that travels away from the simple horror and gore that most things Zombie are related with and focuses on real human emotions and interaction.