The Continuum Transfunctioner
From: Dude, Where's My Car?
Destructive potential: It looks like a Rubik's Cube, but when activated, this mysterious device has the power to destroy the universe and everything in it. It's undetermined whether pulling off all the stickers and replacing them in order can set the process in motion.
What it took to stop it: Two guys that looked like they just walked out of a Berlin night club, a group of weirdos led by Hal Sparks, that guy from That '70s Show, and Stiffler.


The AllSpark
From: Transformers
Destructive potential: In the hands of the Autobots, the AllSpark could actually be used to improve life all over the universe. But in the hand of those jerky Decepticons it could mean the destruction of all life at the hands of a bunch of sentient-but-sadistic vending machines.
What it took to stop it: The entire United States military and a bunch of other transforming robots. Shia LaBeouf's snarky comments also helped degrade the Decepticons' self-esteem.


The Cosmic Key
From: Masters of the Universe
Destructive potential: Skeletor took the humble Gwildor's invention, used it to take over Greyskull, and drained enough power from the Sorceress to become some kind of god. He even got some of his chin and neck skin back, but that didn't stop him from wanting to destroy the universe.
What it took to stop it: If you have He-Man, you don't need a friggin' lawsuit.


The Donut of Destruction (DOD)
From: Spaced Invaders
Destructive potential: Honestly, I couldn't bring myself to waste a Netflix slot on this piece-of-crap movie. But if my vague memory serves me right, this donut-shaped device is meant to explode everything within a million miles of it, while protecting those inside of it. Or something.
What it took to stop it: Lucky for us, the Martians wielding it caused it to fall apart before it could be fired, reminding us all that SkyMall is not the best pace to buy a doomsday device.


The Doomsday Machine
From: Star Trek (The original series)
Destructive potential: Inside its impenetrable neutronium shell is an enormous machine that obliterates planets and uses their remains for fuel. It would blast through the earth and eat its innards like Roger Ebert at a clambake.
What it took to stop it: Kirk made a daring run into the mouth of the beast with the spaceship Constellation and exploded its engines, generating a 97.835 megaton nuclear explosion and cooking its guts like the inside of an outer space Hot Pocket.

Halo
From: The Halo series
Destructive potential: In an effort to keep the ravenous Flood of gross-looking aliens from getting out of hand, the Forerunners created the Halos with the ability to destroy all biomass within a radius of 25,000 light-years.
What it took to stop it: It only took Master Chief a few million rounds of ammo and some impressive warthog driving to rid the universe of the Ark, the Halos, and the pesky Flood. The tens of millions Microsoft spent on marketing didn't hurt, either.

Sustained Fusion Reactor
From: Spider-Man 2
Destructive potential: Doc Ock was looking to create a reactor that could generate the same kind of energy the sun does. The idea could've meant the end of the human race's reliance on fossil fuels, but since the doc was completely bat-shit crazy when he was working on it, it almost destroyed everything around it.
What it took to stop it: Spider-Man was, of course, successful in stopping the machine from roasting the flesh from our bones. But in retrospect, being burned alive probably would've been a lot easier than sitting through the swing dance scene in Spider-Man 3.