The Wrench from Bioshock. Sure, other games had similar weapons, but did any of them look as nice?
I believe it has some obsene name like "an Evicerator" or something. Imperial priests use them in 40K, plus they're a favourite among the Sister of Battle. It's a 6 foot long chain saw with a flamethrower strapped to the bottom. Which, if the stats are anyhtign to go by, was probably then coated in an energy field akin to that of a lightsaber.
Hell, ALL power weapons in 40K, not least because you have all the fighting power of a lightsabre, yet all the style of a godlessly tart and ornate longsword.
Hell, ALL weapons in 40K.