This is a quote from The Terminator .
The Masmune. Anything that makes a White Mage a killing machine is automatically cool.
The Time ship from the Voyager episode Year of Hell.
The hookshot, from The Legend of Zelda. Not so much because it’s useful as a weapon (although it is), but because it’s a multipurpose grabber. Need that thingy over there? Don’t want to get out of your chair? Clank! Shifashifashifashifa… Clunk!
100- foot tall genetically engineered walking kelp with cybernetic enhancements. Admittedly from a story that I wrote, so I might be biased.
Taichkomas from Ghost in the Shell. They’re disgustingly adorable!
A Zinder Nullifier, don’t worry those holes in the reality will eventually go away.
The Master Key/Lighthawk Wings/Lighthawk Sword from Tenchi Muyou! It’s a lightsaber! It’s a personal defense system! It’s the ultimate bladed weapon!
The Holy Hand Grenade of Antioch.
NI!
And maybe the Noisy Cricket, if I need some range…
After some thought, may I change to the Doom II BFG?
Nothing But Gingerbread Left
WWII-era SF story. I don’t remember the author. Germany loses war because someone creates the ultimate “can’t get it out of your mind” song, in German. German army fall prey to ditty; becomes too obsessed / distracted to continue fighting. “Left a wife and 17 children…something, something, something…nothing but gingerbread left.” (Have no fear; song has power only in German. Loses something in translation.)
Along those lines: BOLOS! From Keith Laumer’s series.
30,000+ mt supertanks, armed with 200cm “Hellbore” cannons (think of briefly opening a portal to the heart of a star, and letting it out the barrel aimed at the enemy) dozens of 20cm Infinite Repeater Plasma (point-defense) Guns, anti-personnel clusters, Missiles (with every kind of warhead you can imagine), and most importantly, with sophisiticated positronic AI brains programmed with the sum total of humanity’s military knowledge, and every battle recorded, and a hard-wired personality core that emphasizes Duty, Honor, and Loyalty.
Lightsaber my ass.
A BOLO would crush a Star Destroyer like a beer can under a tank’s treads without even looking up from the Sunday crossword.
The 13mm “Jackal” pistol from the anime Hellsing, and Hellboy’s “Samaritan” pistol. Both are good, capable anti-undead weapons. (Albeit ones that can’t be fired by normal humans.)
The anti-metahuman bomb from Kingdom Come.
The “SOL” platform from Akira.
I’ll always have a soft spot for the laser pistols from Disney’s The Black Hole. Ergonomic, double-barreled design, OK sound effects, and they actually fired beams—a straight line of light instantly appeared between the gun and the target when the trigger was pulled, and disappeared just as quickly. None of that “fire bolts of energy traveling slower than a baseball” crap.
I seem to have posted this in another thread, but what the hell? A board with a nail in it. Second choice: der Happy Stick, forged from a fragment of Thor’s hammer and wielded by the one and only Wulf Sternhammer. A ranged weapon? The Nightmare Gun, from Judge Dredd, which affects the temporal lobes to kill the victim by amplifying any latent fears he or she may possess - the homeless and unkempt Halbert Gumby succumbed to a fear of haircuts: Dredd, of course, had no hidden fears and was the only person immune to it.
{How is it that I can remember in detail comics I read twenty years ago and be unable to remember the fruits of five years at university?}
I would have to second, Stormbringer and it’s twin Mournblade. They feed off souls and augment the wielder.
Shieldbreaker from Saberhagen’s Book of Swords series. Except for that one weakness, which I won’t spoil.
Any of the equipment that the Eldar Harlequins wield in Warhammer 40K.
Caladbolg. Sword from Celtic myth, said to be able to cleave hills in half.
I’d like to second the Lazy Gun
and add Mieville’s Probability Sword, from The Scar
Colourbombs sound good too.
The neuronic whip, appearing in many Isaac Asimov novels. Causes no actual harm, but stimulates the nerve endings intensely enough to cause extreme pain or fainting.
I thought those were Fuchikoma.
Another vote for the Tnuctipun Soft Weapon, as described by Larry Niven. Of course, I’D want the proper code phrases, the ones Chuft-Captain didn’t have.
Failing that, I’d settle for the BFG from Doom.
Illegal Aliens, Phil Foglio: The STOP THAT cannon.
SheVa, from John Ringo’s books. Designed to take out enemy landers at relatively short range. It ain’t a Bolo, but it’s still nice.
Height: 170 ft. ground to top of turret
Treads: four
Tread height: 27 ft.
Tread width, individual tread: 150 ft.
Weight of individual tread: 37 tons
Total vehicle width: 385 ft.
Total vehicle length: 468 ft.
Gun length: 200 ft. including barrel and breech
Gun bore: 16"
Round weight: 16 tons, projectile, cartridge and propellant.
Cartridge length: 14.7 ft.
Cartridge diameter: 27 inches
Reactors: 4 Johannes/Cummings pebble-bed uranium/helium
Drive motors: 48
Total power: 12,000 horsepower
Unloaded weight: 7,000 tons approximate
Standard round: a saboted 8" x 72" DU penetrator with a 10 KT antimatter charge
Also fires sensor munitions and larger antimatter area effect weapons.
Most interesting personal weapon: The Lewitt’s whistling.
I like the Saint Of Killers’ revolvers from Preacher. Made out of an angel’s sword, they never jam, never run out of bullets or require reloading, every wound is always fatal and they can … kill God
Left!
Left!
Left, right, left!
Left a wife
And seventeen children
In starving condition
With nothing but gingerbread
Left!
Left!
Left, right, left!
Repeat until institutionalized.
I don’t know if the pun on “left” used here would even work in German . . .
Something to do with level of interest, perhaps? 
The way it works in the novel is very much fictional, as far as I know.
Well, it sounds like Tachikoma to me, but then again I don’t speak Japanese and I have no idea how good or bad the dubbing is.