Dark Edge of Insanity

Dark Edge of Insanity is a two-handed axe that had the highest melee DPS in the game at the time of its release. It was surpassed in DPS only by Might of Menethil and the Corrupted Ashbringer until The Burning Crusade expansion. The eye embedded within the axe blinks periodically, and will sometimes even rotate within its "socket".

Source
The axe drops off C'Thun, the final boss of the Temple of Ahn'Qiraj.

Trivia
The axe looks similar to Soul Edge from Soul Calibur series.