Warlock's Felguard Pets
Warlocks can get this pet from investing 41 points in the Demonology tree. The Felguard's aggro-holding ability is significantly better than the voidwalker's. This goes for his melee damage as well, comparable to the succubus, and for this reason makes them both obsolete except for sacrifice, seduce, and the versatile Master Demonologist's buffs that these demons grant. His abilities, which must be acquired through purchased grimoires, include a Demonic Frenzy, taunt, cleave, and intercept (which charges an enemy and stuns them for 3 seconds). He is great for PvP and soloing, and can even hold his own in a raid if kept healed. When facing an enemy warlock who has one, it is advisable to banish it, hence removing the buffs this demon gives him.
An effective method of grinding mobs with a Felguard: Attack the first mob, DoT it two or three times while the Felguard builds some aggro, and then let the Felguard continue with the next mob before the first is dead. That way, the Demonic Frenzy will stay at +50% attack power.