I’ll take a Tissue Compression Eliminator, please. And maybe a Morganti blade for backup.
What is the gun with all the spikes etc that Zaphod brandishes against the Krikkit robots in Life, the Universe and Everything?
huh. And here I was for decades thinking Barr was being creative and original.
Well, Barr did take the idea and give it his own spin. Elric never communicated with the souls he took, he just fed on them for physical strength.
Two interesting ones:
The Big Bang gun was a rather interesting device, meant for a PC Champions! group which constantly was out finding bigger and better weapons. Well, the Solar Flare Cannon wasn’t enough. (It fired… Solar Flares.) The Black Hole Projector? Not good enough. (Naturally, it fired Black Holes.) The Graviton Wave Gun wasn’t for them, no sirree bob! (Had no range and acted instantly bypassing any defense except Not Being There.) Same for the Cosmic String Raygun, the Planetary Disintegrator, and so forth. In search of bigger guns, they were rapidly climbing past the “Destroy Planet” into “Destroy Galaxy” levels.
Finally, the GM handed out the Quantum Vortex Projector. This handy dandy device was the ultimate in destruction. It started a new Big Bang which consumed everything spreading out at a rate of lightspeed. There was no defense: it simply ate the universe and sucked in all nearby universes to the Vortex O’ Death. Even Black Holes were utterly swallowed. Heck, even the dead spirits in the afterlife were suckjed in and would eventually have to reincarnate or something.
After receving this item, they looked at each other, realized that not only could they never actually use any of their weapons, but thhat they had finally finished the power scale. There was nothing bigger. They carefully collected all their hideously super-death devices, tossed them into a black hole to be destroyed and emitted as cosmic radiation, and went back to punching out Viper thugs and fending off Dagger.
…
My other favorite fictional weapon was the Wooden Gun. Made by a Buddhist Priest, the Wooden Gun was just that: a peice of wood in the vague shape of a gun. The priest carved it and left it lying around, while various conquerers, kings, and generals picked it up, contemplated it, and then left it lying somewhere for the next person to grab. I suppose metaphysical persuasion through symbolic representation isn’t much of a “weapon”, but it was very effective.
Humorous sword: Lilarcor
Serious sword: Terminus Est
This weapon neither erased history, or destroyed souls. You call that “ultimate”? 
Elric & Stormbringer(1961) vs Katana (1983-ish)? While the mechanics of use are different (Stormbringer merely supplies Elric with strength from sucked-up souls), Stormbringer would be well-enough known, and I can’t think of a prior example of a soul-sucking sword off the top of my head.
Hijack: I’ve never played Baldur’s Gate, 1 or 2. I had no idea Joss Whedon did the writing.
Minsc: What? Boo is outraged! See his fury! It’s small, so look close. Trust me, it’s there.
I loved the Baldur’s Gate games.
RR
Neither/nor; either/or. You can’t mix and match.
Sorry, one of the few grammar hiccups that ever bugs me. 
The Shrike class Light Attack Craft from the Honor Harrington series of books. Basically, they took an obsolete warship class (the LAC, which was too small to mount a fusion reactor, and was thus incapable of hyperspace travel and too small to mount effective sidewall defenses or significant numbers of capital-ship grade missiles; they tended to get swatted like flies in combat against larger warships) rethought some old technology (Fission Reactors, which required less space than Fusion reactors, but could only be made so large), and produced a whole new class of fast, stealthy, well-armed ships that relied on swarming attacks instead of conventional broadside attacks.
The first time they were used in combat, launched from a specially built carrier ship, they tore an enemy squadron of battleships and battlecruisers to pieces.
Of course, the response from their enemy, the Havenites, was to field a class of LACs (the Scimitars) that were outmatched in every way by the Shrikes, but which carried a large battery of nuclear missiles which they would liberally pepper space with in order to take out attacking Shrikes en mass, thus highlighting the difference between the Manticorans and the Havenites. The Manties solve problems with a screwdriver and a set of precision pliers, the Havenites use a sledgehammer and duck tape. And the sledgehammer is occasionally duck-taped onto its handle.
The first thing that came to my mind was the Doomsday Machine from Star Trek. Next was the Death Star.
As I was trying to figure out who would win the “Star Trek/Star Wars Planet Killer Throwdown”, **Rhiannon8404 **gave the correct answer to the question in the OP…
The 1920’s-style “Death Ray”
(Yes, **Ludovic **beat her to it, but I’m ashamed of the first 46 people who posted in this thread. Really…)
Off topic: What series was this from??? I vaguely recall reading it in days of yore, but it rings a bell for no one else I know, and googling that is nigh useless.
On topic: I’ll just take a functional time machine, thanks. Any one will do. Maybe a TARDIS. That way, anybody else comes up with a better super-weapon, I’ll just visit them in diapers.
David Bischoff’s Gaming Magi trilogy, I think.
It is, indeed. Thanks!
The Yamamoto from Larry Niven’s Man-Kzin Wars. Simple concept - take a ramscoop spaceship and launch it from Earth to Alpha Centauri. It arrives travelling close to the speed of light. The magnetic field kills everything in front of it and at that speed it’s mighty hard to hit from any other position. As it whips by the Kzin-occupied planets it just flings quarter-ton blocks of iron at them. At those speeds it might as well be chucking out antimatter.
The whole thing is used as a massive distraction to get two people onto one of the planets - they are in a tiny spaceship, run by a self-aware computer, protected by a stasis field. To slow down they go right through the system’s sun.
Another one which was fictional in the sense that it was planned, construction began but it was never finished is Project Pluto. There’s something so utterly insane about the idea - take a small unshielded nuclear reactor and use it to power a ramjet. Put it in a big honkin’ missile. Accelerate to ramjet speeds with rockets and the ramjet then kicks in. It can stay aloft for months, cruising along at Mach 3, spewing radioactive waste behind it. In attack mode it was designed to fly a few hundred off the ground, using the terrain-following system later put into cruise missiles. So you’ve got a missile the size and weight of a locomotive screaming right overhead at 2000mph spewing radiation. It was designed to carry up to 24 one megaton bombs that it would toss out as it passed over each programmed target. Once done you could then have it fly right into target #25.
Because the basic system was so simple and robust they nicknamed it “The Flying Crowbar”. The project was killed by the development of ballistic missiles and the fact that there was no place to actually test the damn thing.
The flying Hunter Killers from the Terminator series. They had a certain amount of style and class, and in addition to being terribly kick-ass, they looked so cool plowing into the ground when shot down (as with anything, sometimes teh coolest thing about a weapon is how cool it is to watch it blow up)
I also have to admit that I loved the crew-served turbo laser cannons with the energy canisters they loaded for each shot. One of the nice things about Star Wars is the mix of sci-fi with Old School.
I’ve changed my mind, I’ll have a War TARDIS.
That way I can win before my opponent even knows a shot has been fired.
I know that ordnance such as the Death Star are weapons, but firing a huge beam of light at a planet to destroy it just entirely lacks panache, doesn’t it?
It would be remarkable, though, if Barr was not familiar with Elric. I guess I should not complain too much since far worse rip-offs have occurred in comics.
Technically, I could get off by saying it was a mere spelling hiccup. It might even be true. 
And if “real-life, but unbuilt” weapons count, I’ll say…the Landkreuser P1000 “Ratte.”
One can only dream…and dream about type developments and upgrades (How 'bout a Ratte II with 16"/.50 guns, and a fission plant?).
You mean you want a SHEVA from John Ringo’s Posleen invasion books. Bun-Bun was the name of the one he followed in When the Devil Dances and Hell’s Faire. Not only is the tank (Land dreadnought?) nuclear powered, it’s armed with nuclear and anti-matter rounds for its 16 inch cannon, too.