Robocop, and his predecessor that didn’t work so well.
Stormbringer
The powered armor from the book Starship Troopers (if only the movie had had it!). Looks like something similar will be in James Cameron’s Avatar.
The Blade that was Broken, aka Narsil, aka Anduril, aka The Flame of the West.
Now I feel obliged to mention ‘The One Ring to bind them all’. 
Xena’s chakram!
The Colt in Supernatural.
The honking huge gun that Vasquez used in Aliens. It used a Steadicam harness and I wonder if the military investigated mounts like that as a result?
“Gun” from Sledge Hammer. It was not just a character, it was the love interest. See also: “Sweetness” from the Colbert Report.
Zorg ZF-1
The Gatling Gun (multiple Westerns…blew my mind when I saw it as a kid)
The Death Star
The man with the golden gun’s gun.
Indy’s Whip
Mike Hammer’s Colt .45, “Betsy.”
Also… GROND!!!
The Red Ryder B. B. Gun.
The speed of light railgun with x-ray scope, though unlikely, is the only memorable thing from the film Eraser (1996). It started making appearances in unrelated video games. I think Perfect Dark for N64 was the first game to use it.
The Night Slasher’s knife and Marion Cobretti’s .45, a 2-for-1.
Karl’s Steyr AUG from Die Hard.
Honorable mention: the non-existent Glock 7 from Die Hard 2. Not only did it perpetuate the myth that exists to this day, but it became a legendary joke amongst gun owners in much the same way that “hacking the Gibson” is with computer geeks.
nvm, beaten to it
The minigun in Predator.
Goldeneye
+1 Deathstar
Kitt
Transformers
Gundam Wing
Batman’s utility belt
Spiderman’s webbing
Green Destiny (crouching tiger hidden draggon)
+1 Robocop
+1 Indy’s whip
+1 Golden gun
Oddjob’s hat
Yes, Those long rifles are so fun to shoot.
I also can’t believe no one has mentioned James Bond’s Walther PPK yet.
(Yes I know the various book and film Bonds have used many different pistols, but the PPK is the famous one.)
The Krang from The Tar-Aiym Krang. A huge pyramid, which is only the control center for a sentient weapon built throughout the entire planet.
Morgaine’s Changeling, a crystal sword that produces a Gate to nowhere when drawn. A black hole on a stick, basically.
The Swords of Saberhagen’s Swords novels.
The Sword of Bheleu from the Lords of Dus novels by Lawrence Watt-Evans. It influences or outright possess its destined and only wielder, Garth the Overman. The icon of the God of Destruction, it sends forth such things as directable gouts of flame ( enough to blow up buildings after snaking though underground passages; in one case, enough to reduce a godzillalike monster to ash and bones ). It summons storms, controls lightning, creates earthquakes, and defends against weapons and spells.
The gun from I Come In Peace; about the only cool thing in the movie. Big, black, mean looking and it created a chain of explosions as long as the trigger was held down; very spectacular. Seen in use here starting at 6:15.
Th Hellbore main gun of Bolo tanks, as well as the Bolos themselves. Basically, a plasma gun that can destroy starships in orbit from the ground, punch holes in mountains or destroy a city in seconds. Mounted on a sentient tank tough enough that it can survive a hit or two from one, and have designations like “Continental Siege Units”.
The Lazy Gun.
Isilith the Widowmaker of the Horse Lords novels.
Mjolnir, the hammer of Thor.
Demonfang of the Frost novels; a dagger powerful enough to wound a lesser god, tipped with a minuscule gate that sends the souls of those it kills to the worst pits of Hell. When drawn, the screams of the damned can be heard from it.
Sten’s “ultimate knife” from the Sten novels. Kept in an implanted arm sheathe, it is small, lightweight crystal and can cut through a diamond just by being laid atop it with no pressure.
The wild boy’s knife-edged boomerang in The Road Warrior.
Each of the Ninja Turtles’ weapons.