Enderman

The Enderman is a mob that will be introduced in version 1.8; The Adventure Update. The Endermen are depicted as 3 meter tall, black creatures with long arms and legs. They also have the ability to pick up and move blocks around. They are generally peaceful. If you look at them, by placing your crosshair directly over them, they freeze, stare back at you, and become hostile. They stay frozen as long as you keep looking at them. When you look away, they will quickly run towards you; if they are a long distance away, they will teleport several times until close enough to reach you. Endermen can teleport about once per second.

Notch posted a new image on August 2nd, along with some new information on the Endermen.
 * Wearing a pumpkin will prevent Endermen from attacking you.
 * When they have green eyes, they are not aggressive towards the player; when they have red eyes, they are currently hostile.

Trivia

 * The name "Enderman" is a subtle reference to the popular internet phenomena Slender Man, and was given to the mob by Notch in a Reddit thread.
 * Due to the Slender Man similarities, many have petitioned to change the name "Endermen" to "Far Landers". Notch has stated however that he will not change their name, regardless of this petition, going as far as to joke that he should change the name of the Far Lands to "The End" instead.