The Scourge- Originally created by the Burning Legion as a weapon to assist their invasion in the Third War, they went rogue after The Battle for Mount Hyjal and planned to destroy all life on Azeroth. Currently Inactive.
The Forsaken- Broke free from the Scourge and joined the Horde, lead by Sylvanas Windrunner.
The Risen- A faction of Undead in Stratholme lead by Dreadlord Balnazzar, consists of risen scarlet crusaders who plan on taking the Plaguelands for the Burning Legion.
Cult of the Damned- A cult that served and swore oath to the Scourge and the Lich King. Current whereabouts unknown.
Rotbrain Undead- Group of Rogue undead that tried to break away from the Forsaken, currently destroyed.