Dalewind Trousers

Source
Despite not being in this item's normal level range, Ragnaros and Nefarian have a chance to drop it as well.

Removed sources
Other raid bosses that could drop this item but have since been removed include the following:
 * Onyxia
 * Azuregos
 * Emeriss, Lethon, Taerar, and Ysondre
 * Qiraji Lieutenant General
 * Colossus of Ashi, Colossus of Regal, and Colossus of Zora
 * Lord Kazzak
 * Highlord Kruul