Dal'Rend's Sacred Charge

Dal'Rend's Sacred Charge is a rare-quality sword. Prior to the release of The Burning Crusade, it was an excellent main hand sword for rogues because it hit extremely slowly, making Sinister Strike hit very heavily. It is also half of the set Dal'Rend's Arms, with its counterpart being Dal'Rend's Tribal Guardian. The set was also highly sought after by hunters as one of the best pre-raid melee weapon options for buffing ranged dps.

Source
This sword drops off Warchief Rend Blackhand, in Upper Blackrock Spire at an approximate 7% droprate.