Black Dragonscale
Black Dragonscale is usually skinned form Black Dragons and at least level 58. Dragons in the Death Talon clan that can be found in Blackwing Lair. The drop rate of Black Dragonscale in Blackwing Lair is pretty high, so each run will produce heaps of Black Dragonscale.
See below for the maps to farm Black Dragonscale in WoW.