Lightsaber.
The Sword of Shannara
The Wierding Module from the 1980's Dune movie. Holy shit was this weapon badass to me as a kid, still is really. "Chaaaaaaa SAH!" xD
The Swords of the Cross from the Dresden Files. Especially
The Sword of Shannara
Mostly because of how it was used to beat the big bad guy in the first book. It wasn't the super powerful weapon, in fact it was a regular sword in all ways but one. It revealed the absolute truth about things around it. And it killed the big bad guy, because he was already dead. The "lie" was his undead status. He was a ghost, a shadow, an echo of a being long dead. And having that revealed to him at the climax of the story is what undid him. I thought that was an interesting take on the "magic weapon to save the day" trope.
The Wierding Module from the 1980's Dune movie. Holy shit was this weapon badass to me as a kid, still is really. "Chaaaaaaa SAH!" xD
The Swords of the Cross from the Dresden Files. Especially
After Butters gets one, and it basically gets turned into a fucking holy lightsaber. xD