In The Venture Bros., Brock, the tough bodyguard character, often uses anything to kill people (often nearly anyone.) Once he is pinned under a man with a samurai sword in a hotel room, but then Hank opens the hotel room's end table drawer. Brock remembers what a pastor told him earlier that day... "The only weapon you'll ever need is the bible." He reaches in, taking the hotel bible and bludgeoning his attacker over the head.
One episode has Brock kill a group of The Monarch's guys with a lawnmower.
One episode has Brock kill a guy by swinging around a guy who's hand was inside Brock's rectum.
In Archer, he and Lana lost their duffle bag full of ammo in a swamp with a very pissed off, wounded gator. All they had was a cooler full of beer, bottled water, and dry ice (to keep the beer extra-cold!). Lana thought they were stuck with no weapons, until Archer pointed out that dry ice combined with undiluted water in a sealed container (like a closed beer bottle) causes a pressure buildup until it explodes and essentially makes a glass-based frag grenade. Archer is actually correct in his chemistry here, and after some measuring trials, they are ready for the gator, but they never get to use one on it as they run out of bottles by the time the figure out a combination that will be destructive enough but still safe enough to deal with.
Tom and Jerry has the the eponymous cat and mouse making constant use of this trope.
The show Jackie Chan Adventures pays obvious homage to Jackie Chan's movies, as the hero can and will use whatever is at his disposal. The first of many examples of this has Jackie defeating three mooks armed with high-tech weaponry, with a pair of wind-shield wipers.
"Diiid we mention he had windscreen wipers!"
That's barely the tip of the iceberg. He once trounced a guy with a soup spoon and a toothbrush
Heck, he once used a secret agent that had been knocked outas a weapon!
Any character with some sort of telekinetic powers will use this trope to hurtle stuff at the bad guy.
This sums up the "Propel" attack in City of Heroes. Extra hilarity because the projectile looks like a different stock object to each player, due to a programming quirk.
The object is fully random, but occasionally funny events occur like a vampire being KO'd by a speeding coffin.
In the Justice League Unlimited episode "The Great Brain Robbery", Flash and Lex Luthor swap minds. While trying to fend off his pursuers at the Watchtower, Luthor, in Flash's body, runs to the cafeteria and starts throwing food at them. At first it seems useless, since Green Lantern has created a shield around his teammates to avoid being hit. Just then, he picks up a dish filled with yellow pudding and throws it at him... And the pudding easily goes through the shield and splats GL squarely in the face! This is due to the one great limitation of GL's power ring: it doesn't work on anything that's yellow (since it symbolizes fear, which is the essential opposite to willpower, whose token color is green).
Brainilex:having disposed of the rest of the League without slowing down his data transfer "...now where is Wonder Woman?" cut to Javelin toss. Explosion ensues.
This trope is taken to the extreme when Batman uses the Justice League Space Station to take out a gigantic thanagarian wormhole-generator by destabilizing it's orbit and then manually steering it to it's target.
Which is similar to him steering a giant toy robot into a kryptonite Asteroid in Superman/Batman: Public Enemies.
Prowl of Transformers Animated occasionally improvises; in his first fight against Lockdown, he came at the bounty hunter with a metal pole he picked up from a pile of scrap, and his toy comes with a traffic light he can use as a mace.
Most of the Autobots in Animated were part of a repair crew, and as such have power tools instead of dedicated weapons. Even Optimus Prime's axe goes with his fireman theme rather than being presented as a straightforward implement of harm.
Dinobot from Beast Wars manages to smack the MacGuffin out of Megatron with a stick with a rock jutting out of it. One of the proto-humans winds up using this as a weapon/tool.
Megatron: Face it, Dinobot! You're old technology, obsolete. What could you possibly do?
Predaking of Transformers Prime didn't really need to use an improvised weapon due to his massive strength but at one point he starts beating Megatron with one of his own Vehicon troopers.
Any of the handful of "real world" battles in Code Lyoko apply, since the characters are Middle School students, and swords aren't exactly commonplace. However, Odd and Jim gain a special commendation for shooting monsters with a nailgun in the last episode of Season 1.
See also the Season 3 episode "The Pretender", where Ulrich, after losing his katana to a swarm of Frelions, still manages to destroy three of them and a Manta with a shard of virtual stone.
In one episode of the 2003 Teenage Mutant Ninja Turtles, the turtles are imprisoned and stripped of their weapons, and therefore have to resort to fighting with cleaning supplies. They manage to take down a whole squad of alien triceratops guards this way, with Raph, of all turtles, getting in a Shout-Out to The Tick: SPOOOON!
The Tick himself went up against super-strong Baron Violent, who threw a car he crushed with his bare hands, and then threw a big slab of pavement. It landed on The Tick's "dog" Speak, leaving him untouched but prompting The Tick to run him to the vet, hysterically shouting "BAD-MAN-HIT-DOG-WITH-STREET!!!"
Parodied in The Simpsons. Bart is pinned down in a scuffle with Milhouse, and starts groping around behind him for something to use as a weapon. His hand passes over a brick, a broken bottle and possibly various other suitable objects, and settles instead on a Magic 8-Ball.
Also, a recently-fired Chief Wiggum attempts to rob Homer at gunpoint, but it's revealed that the gun has no firing mechanism. He continues to threaten Homer anyway: "I can throw this pretty hard."
In "Bride of the Pastmaster", the SWAT Kats are Trapped in the Past without regular ammo, so they trick out their Cool Plane the Turbokat with whatever's at hand, including pepper stew.
The SWAT Kats' civilian ally, Deputy Mayor Callie Briggs, may not carry a weapon, but she's been known to attack supervillains with a money bag ("The Wrath of Dark Kat") or her briefcase ("The Ci-Kat-A") to defend herself or her friends.
In the first S-Force episode of Megas XLR, Coop is surprisingly able to take down two of the members of the group without his mech. His weapon of choice is a novelty talking fish.
In Lilo & Stitch, Stitch uses many household objects in a fight, and makes a doll into an IED.
On Dastardly and Muttley in Their Flying Machines, Klunk must use resources at hand to create aircraft for the Vulture Squadron in "Have Plane, Will Travel." He also turns crashed airplanes into a flying dump truck in "A Plain Shortage Of Planes."
In Thundercats 2011, when Grune and Pantro were once cornered by a Giant Spider, Grune ripped his own fang out of his mouth and stabbed the spider to death with it.
Thanks to his training the titular Samurai Jack is a master of using anything as a weapon. If he can pick it up and swing it, it's a staff. Break it in half and he'll just wield the two halves with just as much mastery.