Blizzard have unleashed the Monk on the Diablo III: Darkness Falls, Heroes Rise page. As with the Demon Hunter and Barbarian we get a short story, a spotlight video showcasing the Monk, a chance to win some cool prizes and the exclusive Class Sigil.
The monks. Holy warriors who believe that the madness and chaos of Sanctuary are destined to be brought into order, and that it is their sacred mission to assist their thousand and one gods in doing so. Arrayed in the fiery colors of Ytar, the fire god, monks draw from their years of intense training and meditation to become masters of melee combat. While proficient with many types of weapons‚ Aistaves, blades, maces and spears, monks have no real need for such crude tools. Their discipline has honed both body and mind into living instruments of divine justice.
The Monk got a background-building short story as well, which you can read here.