Quel'Serrar

Thunderfury waiting room.

Aside from the Thunderfury this was one of the best tanking weapons in Vanilla. To get the weapon you must first get the stupidly rare book "Foror's Compendium of Dragon Slaying" that dropped out of Dire Maul either off bosses or Dusy Tomes (books on the ground). The questline ends with you needing to have Onyxia breathe fire on the blade when you stick it in the ground and then defeat her.

It is no longer available in game but in Wrath Blizzard added 2 swords with the same model to the anniversary re-do of Onyxia25.

In Wrath there was also another quest sword named Quel'Delar that looked similar but arguably not as cool.