It’s never time for the Bloody Card.
I’m quite fond of Sergeant Schlock’s plasma cannon, from Schlock Mercenary. You know, the one with the sound effect that goes “Ominous Hummmmmmmmmmm”. 
I want a bowel disruptor so very badly.
Not quite a weapon, but I would love to have some of Robert Heinlein’s Powered Armor.
I’ll probably mess the quote up a little, but…
“We wanted a boojum and all you give us is this… snark?!”
I can’t remember which book used this Carroll reference either. Sigh!
26 posts and no one’s said “lightsaber”?!
What is this place coming to?
Who among us can say he doesn’t enjoy seeing the peasant girls cower in fear when he whips out his Rod of Lordly Might?
Ash’s shotgun from Evil Dead 2 and Army of Darkness ("S Mart’s top of the line).
Load it with Unerring Shells of Neverending Capacity and reload only when necessary for dramatic effect…it’s the adventurer’s ultimate weapon.
Hail to the king baby.
A batarang, if it’s prepared.
They are basic and probably quite old, but I am always in awe of the horrific stopping power of the Gunslinger’s six-guns from Stephen King’s Dark Tower series. When handled by the Gunslinger, they are always deadly accurate. You always know that when bullets start flying, someone is going to meet a very unfortunate end.
I am kind of partial to the Crom Feyr from BG2:SoA and BG2:ToB. If upgraded right its a +6 Warhammer that gets incredibly many criticals and is a one handed weapon. If you gave it to Minsc and developed his warhammer abilities he was bloody unstoppable. Good stuff
The modified TR-115 shown in DS9’s seventh season is pretty cool and one of my favorites – it’s a projectile weapon and can shoot through walls with a mini-transporter attachment to the barrel. If they could make displacement phasers, it’d be the coolest weapon ever.
Failing that, Iron Man’s pretty awesome too.
Certainly I’m not the only person on the SDMB to know of the cohe wand?
-Joe
I’d vote for Unicron, the planet-eating demigod, but I don’t think he’d take kindly to being called a “weapon”…
I’ve always been partial to the weapon from Larry Niven’s short story “The Soft Weapon”.
It’s a shapeshifting, multifunction handgun. One setting provides an energy shield. One is a flamethrower that could double as a rocket engine in space (if you could hold it steady). One is a slug-thrower. One is a matter-energy conversion beam with nearly unlimited range (very dangerous to use while on a planetary surface; there was speculation that this setting was meant for destroying cities from orbit…yes, with a pistol). And one is…well, that would be a rather large spoiler. And it was intelligent.
How about Mankiller from The Misenchanted Sword?
It could only be drawn by it’s owner. Once drawn it would act to kill a man. Not a woman, not an animal, not a demon, only a man (hence Mankiller). Once it had killed a man, it became a normal, even substandard sword until it was inserted into it’s scabbard again.
The owner would do this 100 time (give or take one) and then he couldn’t draw it, only someone else could. That person would then kill the previous owner and become the new owner. Same rules apply except that this owner would kill one less person. Eventually, someone would draw the sword, kill the former owner, kill themselves then the sword would be normal. Also, the current owner could not be killed until his time with the sword was over. Mind you, he could be hurt, just not killed.
I just loved all the rules on this thing.
Chaz from Sluggy.
Unpowered, it’s capable of making its owner into a formidable swordsman. Powered, it’s an intelligent, talking sword that can kill pretty much anything out there and advise its owner regarding how to do so.
The only catch is that it’s powered by the blood of the innocent…
A powergun from David Drake’s Hammers Slammers.
Of course, I’d need someone to follow me around narrating graphic descriptions full of bleak metaphors of my kills.
If I can upgrade, a Slammers iridium armored fusion powered supertank armed with a 20cm powergun would be nice for the morning commute.
What? No mention of the Illudium Q36 Space Modulator?