The Vita-Saw, an older weapon from the TF2 community, is interesting as it shares many resemblences to things from Bioshock.
Ingame, you will meet little girls known as "Little Sisters" who carry a needle that looks like the Vita-Saw.
In Bioshock, there is something called a "Vita-Chamber" which is effectively the place where you respawn when you die with a little Health and EVE.
The Vita-Saw leaves a bit of Ubercharge after you die as Medic.
The two weapons also share strikingly similar appearances.
(Sorry for the small picture, the source has a good image thats actually rotatable!)
And due to the weapons appearance, Valve actually contacted 2K to put the weapon in the game to prevent copyright issues, this is why the weapon is not sold in the Mann Co. Shop.