Blackingwing Lair, home to Nefarian, son of Neltharion, and a host of pseudo-dragon type monsters. Second along the path of 40-man dungeons, this is the stepping stone to Ahn'Quiraj and the beginning for those who have completed Molten Core.
Blackwing lair as you may well have noticed focuses upon dragon-type monsters, nearly every boss being some form of drake, dragon, or half-dragon. Also these dragons specialize in a rather nasty form of attack, shadowflame. Be sure to bring along quite a few Onyxia Scale cloaks before attempting to face down Blackwing Lair
From the World of Warcraft Site:
Blackwing Lair can be found at the very height of Blackrock Spire. It is there in the dark recesses of the mountain's peak that Nefarian has begun to unfold the final stages of his plan to destroy Ragnaros once and for all and lead his army to undisputed supremacy over all the races of Azeroth.