After defending Thunderbluff from the elemental invasion, queue for Gahz'Rilla and kill him. After Gahz'rilla dies you then head outside of his sanctum through the north-east door, follow the hallway, then head east into what is typically the Zombie room in ZF. Go up into the little room with the cauldron, and loot your jackpot! Witch Doctor's Chest! You won't have any competition for the loot inside, and you can keep it all for yourself to use or sell! It has a chance to drop a bunch of different lvl 40ish items and even some blues!
It's also rumored that the rarest item in the game, Spellshock Leggings, could drop from that chest. (Sellable for upwards of 200,000g to the right buyer)
Happy Hunting!