TOS- The phaser assault rifle used in "Where No Man Has Gone Before". Used one time during the whole TOS, we never see it again.
TNG- Worf's collection of Klingon Weaponry
Bonus (what I would like most of all): In the Wrath of Khan, when they beam down to the planet, to find the survivors of the station, Kirk is wearing a red/white starfleet jacket (it's the one he's wearing when he shouts 'Khan' into the communicator. I wanted a jacket like that ever since I watched the movie.