Zombie: You can't have a game with monsters and not feature zombies. Minecraft's take on the shuffling dead is about what you'd expect, they travel in groups and make moaning sounds, although zombies in the game are actually quite fast. They aren't, however, very smart
Zombies will actually walk into water, off cliffs and into other dangers while trying to reach you, so it's not hard to trick them into doing something that's not in their best interests. Defeated zombies will drop feathers that can be used to make arrows.