Off hand items

SKULL OF IMPENDING DOOM
Use: Increase your run speed by 60% for 10 sec, but deals damage equal to 60% of your maximum health and drains 60% of your maximum mana over 10 seconds. (5 Min Cooldown)
An item that can kill you if you are not careful, you just have to love it. It takes a bit of effort to get this however, with a questline starting with an item in a chest in Uldaman, the Tablet of Ryun'eh.
For Alliance this tablet starts:
Solution to Doom; To Ironforge for Yagyin's Digest; The Star, the Hand and the Heart; Forbidden Knowledge
For Horde this tablet starts:
Solution to Doom; To the Undercity for Yagyin's Digest ; The Star, the Hand and the Heart; Forbidden Knowledge
The quest Forbidden Knowledge will reward you with this beauty.