Argent Avenger

Argent Avenger is a one-hand sword with a chance to increase attack power against undead.

Source
This item is a quest reward from The Argent Hold (quest) which starts with Lord Maxwell Tyrosus in Light's Hope Chapel in Eastern Plaguelands.

Notes and trivia

 * The Argent Avenger has jokingly been called a lightsaber by many players in WoW, because of its "energy blade". It can also be enchanted Demonslaying or other "glowing" enchants to give the lightsaber different colors. The Icy enchant is a good way of turning this item into a "facemelter."
 * Is a tribute to the iconic Jedi swords, lightsabers. It can also be transmogged!