What Have We Ear?

Stock trope of the Stage Magician, sometimes refered to as the Miser's Dream. On their introduction, something will get pulled out from behind someone's ear.

This is in fact a very easy trick to perform off-the-cuff. The only setup required is that the magician have a coin or other small object somewhere he can palm it.

For other stock tricks, see Saw a Woman In Half, Pull a Rabbit Out of My Hat, and Disappearing Box.

Examples of What Have We Ear? include:

Comic Books

Prof. Calculus does one by accident in Flight 714.
In a flashback, it is revealed that Jean's mental powers were inadvertently coming to, tearing down the mental blocks Professor X had placed there years before. To discover the cause, Professor X reaches behind Jean's ear and pulls out... a mental hologram of Cyclops, explaining that the resurgence of Jean's powers was due to her trying to emotionally "reach out" to him. Not quite a quarter, but pulling something out of someone's subconscious seems like a cool trick, too!
Mandrake the Magician teaches a kid this trick to get back from a very far future where he had been pulled by that same kid playing with Time Travel. In said future the only thing worth anything is knowledge - and since said trick had been completely forgotten in the face of more advanced amusements, it was very valuable.

Film

Robert does it to Giselle in Enchanted.
In Time Bandits, King Agamemnon does this to Kevin as part of a Cups and Balls magician's trick.
Andy does this to Trish's youngest daughter with a fake ear in The 40-Year-Old Virgin. She is unimpressed, and quickly realizes the implication that he would've had to have a fake ear in his pocket all day just to do those kinds of tricks.
In Night at the Museum, Larry does this to Atilla the Hun. Being the primitive savage he is, he falls for it.
In Merlin, the titular wizard is asked by a young Morgan Le Fay to "Do some magic for me!" He obliges by doing this trick. Her response? "That's not real magic. That's just a trick. Anybody can do that." Which she then proves by pulling another coin from behind Merlin's ear.
- If you pay attention, you notice that Merlin conjures the coin into Morgan's hand with real magic, but she doesn't notice, apparently assuming that's how the trick works.
In Home on the Range, show cow Maggie is able to pull out stuff (food) from the ears of others and herself. Sometime later, Mrs. Caloway teases her on getting some money this way when they and Grace decided to go to town and negotiate with Buck.

Literature

Professor "Reg" Chronotis does this as a hobby in Dirk Gently's Holistic Detective Agency by Douglas Adams. Then he goes on to do something that actually "is impossible".
The Heavy Metal story "Secret of the Coin" had a man take this way too far after it was performed on him as a child, to the point of killing people and finally summoning Beelzebub in order to learn the trick.
Sheriff Pangborn is shown doing this at least twice in Needful Things, by Stephen King, both times to cheer up someone who needs it.
Fake Jamaican Robert Marley pulls this off in John Dies at the End twice. On the first time it's with a live centipede out of David's ear; on the second, it's a live centipede out of his stomach!
Shadow does coin tricks, including this one, throughout American Gods, as a way of keeping his hands busy. It becomes important to the plot when he ends up with a pair of very special coins: the sun and moon.

Live Action TV

Hotel Babylon
On Friends Monica hints to her dad that she needs some money. He's oblivious to the request, and does the coin trick to nobody's amusement but his own. Monica's reaction? "You got anything bigger back there?"
Dax does it to the (large eared alien) Quark in an episode of Deep Space 9. This being The Future, he accuses her of using a teleporter to do it.
This was used in an episode of Night Court to free a Pacific Island princess from an arranged marriage.
JD does this in Scrubs. To no less than David Copperfield himself. Who then promptly makes the coin completely disappear, with a thoroughly unimpressed look on his face...
Jonathan Creek does it also, quite naturally as he is a magician's assistant by trade.
A favorite trick—sorry, illusion—of amateur magician GOB Bluth on Arrested Development.
Happens in the Drake and Josh Christmas special, when Josh has been arrested and is in a jail cell with a Scary Black Man.
- In the episode with the magician, Josh tries to pull the What Have We Ear? trick on him... to be horrified when the coin comes away dripping fake blood.
DJ Jesús does this in one episode of Lucy, the Daughter of the Devil in a way that's genuinely supernatural - the setup is exactly the same, but he pulls an entire platter of fish out from behind Lucy's head, something he couldn't conceivably have palmed (and wouldn't have had any place to hide behind her). Everyone takes the sight with casual disinterest, except for his Yes-Man, Judas.
Big Howard does this to Little Howard in Little Howard's Big Question. Little Howard then goes to try and break his head open to get the money that is obviously in there.
On 3rd Rock from the Sun, Mary's brother Roy tried to impress Tommy with this.

Roy: Hey, what's that? A quarter?
Tommy: Oh, I get it. You're trying to impress a youngster with what you think is a mystifying feat of trickery.
Roy: Cut your hair, you look like a girl!

On Psych, a woman does this with a flower to convince a little girl that the flower was magic. Turns out to be a Chekhov's Skill, as she used to similar trick to steal the ring that Shawn and Gus had been hired to find.
The X-Files. Scully does this to Mulder when they're visiting a town of sideshow freaks and performers.

Newspaper Comics

When Calvin's dad did it to him, he had Hobbes hold him upside down and shake him, to see if there was any other loose change in him.

Video Games

This can get downright repetitive and annoying in Apollo Justice: Ace Attorney. Even worse, any time you present irrelevant evidence to one of the magician characters, they decide to do a trick with it. Usually making it disappear. Understandably Apollo never lets them do it.

Web Comics

Ozy and Millie does it here.
In Thunderstruck, the magician Saxony Canterbury does this trick to amuse a child. Then an assassin tries to shoot him. Saxony catches the bullet in his hat. Then "pulls" it from behind the assassin's ear - still moving. The assassin's head is Chunky Salsa.
An adult version appears (NSFW) in Sexy Losers, where a magician is fingering his girlfriend, then pulls out a coin.

Western Animation

"The Dingo's Guide to Magic" from Taz-Mania.
Dr Henry Killinger from The Venture Brothers, despite the fact that he is capable of very powerful magic, does this to entertain children.
Mumbo pulls a penny out of a hostage bank teller's ear in Teen Titans. The real trick is that it was covered in ear wax...
SpongeBob SquarePants pulled a Krabby Patty out of Squidward's ear once, as well as his nose.
Dexter's dad does this in Dexter's Laboratory when he wants to go buy ice cream from the ice cream truck (whose driver had a grudge against him).
On Aqua Teen Hunger Force, when Frylock is looking for someone to resurrect Master Shake, one of the applicants is a stage magician repeatedly pulling the same quarter out of where Meatwad's ears would be, if he had any.
In The Simpsons, Moe entertains Maggie by pulling a penny behind her ear...who then proceeds to grab the penny and swallow it.

Moe: Okay. We won't tell no one about that.