Hollywood Magnetism

In Real Life, the strength of a magnet's pull decreases over distance, much like radio waves, sound, and (for astronomical distances) gravity. This is frequently forgotten in fiction; not only are magnets selective in what they attract, they're also selective in how they attract it: They have effectively unlimited range, and can attract metal with the same force from any distance.

Another thing to note is that objects under a magnetic pull tend to close in on the magnet at a constant rate of speed, rather than accelerating over time as they move.

In video games, applications of magnetism are functionally similar to Inconveniently Placed Conveyor Belts.

In comedic works, the Rule of Funny will often take precedence.

Subset of You Fail Physics Forever and Sister Trope to Selective Magnetism.

Anime and Manga

 * One Piece may have an aversion in the person of Eustace Kidd, who has magnetism powers; the main way he uses them is magnetizing multiple objects together in chains (like you can do at home with paper clips) to give himself Combat Tentacles. It's played straight when he uses his power to wrest guns from peoples hands.

Comic Books

 * In the British newspaper comic The Perishers, there's a strip where Wellington is demonstrating a magnet to Marlon, and he turns it backward so it will repel things. In reality, magnets will only repel other magnets, and only when their like poles are facing each other.
 * Archie Comics once had a story in which Archie acquired a very large magnet, which he carried in the back seat of his car. As he and Jughead traveled, the magnet attracted anything and everything that was made of metal.

Film

 * Top Secret: Dr. Flammond develops the Polaris magnetic mine. Instead of being attracted to ships and blowing them up like a regular magnetic mine, it's so powerful it drags ships to itself from hundreds of miles away.
 * Parodied in Who Framed Roger Rabbit?, where Eddie uses a large toon magnet to try and wrest a sword off Judge Doom's hands, the magnetic force depicted as lightning bolts that literally grab the sword and pull it.
 * In Indiana Jones and the Kingdom of the Crystal Skull, when Indy needed to find the location of a magnetic crate, he threw gunpowder in the air and watched which way it moved. Later on, this trope is lampshaded when an object attracts gold coins.

Live Action TV

 * The MythBusters proved that magnets can't deflect a bullet, as in Live and Let Die.
 * On Get Smart Sigfried used a giant magnet to pull the entire Seventh Fleet to his island.
 * In the Look Around You episode "Sulfur", they test to see whether sulfur has any magnetic properties. So they use a sheet of paper to "shield" the sulfur from the magnet until everything is in place.

Video Games

 * The magnet gloves in the gameboy color The Legend of Zelda Oracle Games. All objects which you can attract towards you/pull yourself towards are not only magnets, but monopolar magnets (the gloves switch between a north and south magnetic charge so you can push and pull). Nothing else is affected by them.
 * The gimmick for the Goron Mines in The Legend of Zelda Twilight Princess revolves around using the Iron Boots to walk around on areas of magnetic ore in the walls. That's plausible enough. What's not is that fact that in some places the ore emits some kind of superstrong column of magnetism that will pull you onto the wall if you fall into the beam with the boots on.
 * Well, plausible until you realize that even if you don't have them equipped, you still have to be carrying them, and would be subject the exact same attraction. It's the same thing with earlier games and having the boots allow you to sink in water and walk on the bottom, but once you take them off, you're magically lighter.
 * In Mega Man 3, Magnet Man is able to pull Mega Man in towards himself whenever he activates his magnetic field. It'll pull Mega Man in at the same speed regardless of your location on the screen.
 * Justified in Mega Man Battle Network 2. As this takes place in the cyber world, where the rules of physics are constructed of data and are therefore artificial. There's a chip called MagLine which pulls you to the panel(s). If the panels are in the lower row, the staying in the upper row will prevent it from dragging you to that panel and visa-versa.
 * Also, the Battle Chip of Magnetman EXE uses his North-South Tackle, and will not work if there is no room to summon South.

Western Animation

 * The Simpsons: One prank Bart pulls involves two pieces of metal in the bottom of Principal Skinner's shoes and a pair of horseshoe magnets under the stage, which Bart manipulates to make Skinner do a wild dance. In reality, the magnetic field wouldn't be strong enough to pass through that much wood.
 * In the Classic Disney Short "Donald and Pluto", Donald Duck is a plumber who uses a magnet to retrieve his tools from atop a ladder. Pluto ends up accidentally swallowing the magnet, and spends the rest of the cartoon dealing with the various objects that are mysteriously following him around.
 * Wile E. Coyote got bitten by this once. In his attempt to catch Bugs Bunny with an iron carrot, his super-magnet ended up attracting all sorts of metal junk instead, including the Eiffel Tower, an ocean liner and finally a ballistic missile, which blew him to kingdom come.
 * Another Looney Tunes short, "Bugsy and Mugsy", culminates with Bugs putting roller skates on a tied-up Mugsy, then using a magnet under the floor to move Mugsy around...and slam him repeatedly into Rocky. This, of course, won't work for the same reasons The Simpsons example above won't work.
 * In the Superman (1940s) episode "The Magnetic Telescope", the title device is used to drag comets in space down to Earth.
 * In the 1974-74 Superfriends episode "The Shamon U", a Mad Scientist creates small asteroids of gold out of space dust, and draws them to Earth using a "special gold-attracting magnet".
 * In the pilot episode of Phineas and Ferb, Dr. Doofenshmirtz builds a magnet so strong it even attracts aluminum, a metal not normally known to react to magnetism.
 * In the Tom and Jerry episode The Framed Cat, Jerry gets Tom to swallow a magnet and then drills a screw into Spike the bulldog's bone, so the bone flies at Tom from clear across the yard to make it look as if Tom's trying to steal it.