Although he doesn't have a specific Weapon of Choice, Terrence of KateModern usually favours fairly improbable weapons, ranging from an ordinary stick to a freezer van. Occasionally these are improvised weapons, but more often than not they aren't, and you get the impression he's just enjoying himself.
Chaka uses regular playing cards and some forks. Lancer has a pair of paper swords (which he can cover with his PK field, making them incredibly dangerous). Generator has a Hello Kitty compact which is not at all what it seems, weaponized hair decs, and a stuffed cabbit that has taken down grown men in armor.
A very popular phenomenon among fan-created characters for existing series. Yes, that double-ended scythe or windmill-blade-katana-thing your OC has for a Bankai/Soul Resonance/Innocence/whatever may look cool in that one picture... but it would be an absolute pig to wield in an actual fight.
Drake from New Divide uses a flute as his weapon of choice.
In Elemental Wind Elemental Selah uses the sharpened edge of her shield as a weapon. Another character fitting this trope is Corah, who wields a farmer's scythe.
Agents in the Anti-Cliché and Mary-Sue Elimination Society use a lot of different weapons: Claire uses pinecones, Marcus sometimes uses an umbrella, Tyler uses a three foot long Lego axle, Tom uses a shrubbery, and Stephen once beat a Sue into submission using a payphone.
In the fifth episode of the Stickman Can't Fight series, Black uses a hula hoop.
Hitler's pencil in Hitler Rants. Nicknamed the "Pencil of Doom and Mass Destruction", it has the powers to completely blow up a planet. The funny thing is that the powers are activated by banging it to his table.
207. The following weapons are not legal choices in a duel: Steamroller, Nerve Gas, Landmine, Midget.
425. Chainsaws and butter churns filled with bees do not use the same weapon skill.
1680. The point of the Improvised Weapon Skill is not to see how many different things I can kill people with.
1915. The following are not acceptable specialties for a weapon master: Mustard Gas, Cheese Grater, Sardonicism.
2098. Even if I took it with me with the full intention of using it, a manhole cover counts as an improvised weapon.
2290. Even if the rules allow it, my gladiator's starting weapons cannot be the trident and bagpipes.
The soldiers in Shock Troopers make use of a defibrillator to shock enemies, blast them dozens of feet into the air, or set them on fire.
The main weapons of Psycho Gecko are a laser potato peeler, rubber chicken grenades, and a rocket saxophone. In the past he has used a bone shard from the stump of his hand to kill someone.
In Unnatural Selection, this is encouraged by the RPG-Mechanics Verse: Damage is determined solely by the user's offensive stat (making the character's "weapon forms" purely cosmetic combat-wise), but usability as a tool actually depends on the weapon form. As a consequence, most characters will have at least one weapon form that's a tool, musical instrument, etc.; protagonist Alison's first two weapon forms are her hair and a piano.note Usability is based on weapon form, but NOT efficiency: The latter depends on the user's offensive stat too, meaning a DPS brute with a screwdriver will drive in screws faster than a weaker character using a power drill with screwdriver attachment. The weapon form merely means that they're both able to do it.