Seinfeld Season 8 Episode 16 (Episode 150)

George (Jason Alexander) receives a new keychain from George Steinbrenner due to Phil Rizzuto's induction into the Baseball Hall of Fame, only to lose it while jumping over a pothole, which has been paved over. Unwilling to pay the city's maintenance crew, George decides to get his key chain himself. Wearing construction gear and using a jackhammer, George accidentally hits a water main while digging, causing his key chain to fly into the air as well as sending water up Jenna's (Jerry's girlfriend) toilet, soaking her.
 Description taken from  http://seinfeld.wikia.com/wiki/The_Pothole

The keychain when squeezed says "holy cow". After it was paved over, the keychain could be heard every time a car drove over it.

Dead Man Down

Victor aka Lazlo, played by Colin Farrell,  receives a chartreuse rabbit's foot keychain from Beatrice, Noomi Rapace.  It becomes an important symbol of their relationship throughout the movie.  She corrects Lazlo on the color telling him it is chartreuse.  He replies "but rabbits don't come in chartreuse."  Later in the film the villains receive the keychain and one of them wears it on his shirt cuff.  Colin Farrell's character makes sure to get the keychain back when the fighting is done. 

Weekend at Bernie's

Bernie owns a boat and with any boat the owner has keys for it.  Bernie's boat keys are on a yellow floatie keychain with blue writing.  They can be seen a few times throughout the movie.    In this scene Larry and Richard are trying to get off Hampton Island in Bernie's boat.  His keychain can be seen on the console.

Almost Human Season 1 Episode 3

In this cop drama set in 2047 locks with physical keys are a relic of the past.  But the woman in the beginning of this episode likes to keep the old technology and not opt for "bio locks".  She forgets her keys in her office door again and a security guard with a package for her gives her the keys back.  She has what appears to be a green alien keychain. 

The World's End

In this Sci Fi comedy the main character Gary King, played by Simon Pegg, gives up his keys after a few too many drinks and when things were looking bleak.  He has a black skull keychain and another which appears to be for a car brand.  I can't tell but it is a blue medallion on a leather fob. 

Dexter

There are several keychains featured in this showtime drama about the serial killer with a code Dexter Morgan, played by Michael C. Hall.

1.  Season 1 episode 5.  Dexter is investigating a possible target who is a human trafficker and murderer.  Dexter notices his red floatie keychain, concludes he must have a boat, and comments on it. 
2.  Season 1 episode 8.  Dexter received a note from another serial killer he admires, the ice truck killer, in the form of a doll.  Dexter took the doll's head and turned it into a keychain.
3.  Season 1 episode 10 The police department receives a message from the ice truck killer in the form of a jar of blood, blood he got from his victims.  In the jar is a hotel room keychain.  The police go to the hotel to investigate. 

R.I.P.D.

Nick (Ryan Reynolds) just died and finds himself in front of Proctor (Mary-Louise Parker) who inducts him in the Rest in Peace Department, R.I.P.D..  She gives Nick his equipment.  She also has a keychain which appears to have R.I.P.D. written on it.  It might be a locker key or the key to her desk but it is not shown again in the movie.  The keychain is a brass colored circle.

Luther

From the BBC show Luther season 3 episode 3, the show stars Idris Elba.  A man has a very nice white rabbit's foot keychain.  It has a gold colored chain and cap. 

Day Watch

This Russian supernatural movie has a rat character keychain featured in it, it seems to be made of brass.  The main character switches bodies with someone and has trouble fitting the key into the ignition of her car since he is not used to driving it.

Psycho III

The poster of Psycho III features a very prominent Bates Motel keychain to room 1.  Norman Bates, played by Anthony Perkins, is holding the keychain as if welcoming you to the hotel.

The Wire

Bubs is a drug addict turned informant.  He goes with his friend to a court mandated narcotics anonymous meeting (NA).  NA gives out colored keychains to those who have been sober for certain amounts of time.  Bubs takes a 24 hour keychain, symbolizing his desire to get clean.

Detective James Mcnulty is having dinner and places his keys on the table which have a bullet keychain on them. 

Pokemon X/Y

In the new Pokémon games (X and Y), to be released October 12 2013, there will be a new Pokémon, Klefki.  It is called the Key Ring Pokémon. 

The Pokedex description is as follows: "It never lets go of a key that it likes, so people give it the keys to vaults and safes as a way to prevent crime."

Family Guy

To convince everyone to join the tea party (which is actually a front for big business) Carter Pewterschmidt throws arm fulls of "stupid awesome keychains" into the crowd.  A man picks one up and says "oh, my God.  It's the keychain from the dream."

Season 10: Episode 21 Tea Peter

Goldbergs

Barry, the oldest son, is learning to drive and his grandfather is learning to live without driving.  The grandfather gives his keys to the eldest girl and barry gets keys to drive the car.  The keychains featured are a Cadillac logo keychain and a blue rabbit's foot.

Season 1:  Episode 1

Memento

The main character Leonard, played by Guy Pearce, is staying at the Discount Inn.  His room key and its blue keychain can be seen several times throughout the movie. 

Back to the Future

The keys to Doc Brown's time machine Delorean have a keychain with the doc's name and address written on it.  The keychain is a ball chain style.

When Marty returns to the present he finds his life and family's life has been changed.  He now owns his dream truck.  His keychain can be seen when Biff hands him his keys and keychain.  His truck is a Toyota but I can't tell if the keychain is for a Toyota.

(There is one other keychain in this movie and I will post them if I can get screenshots)

Psycho (1998)

Vince Vaughn plays Norman Bates in this 1998 remake of the classic Psycho.  The motel keys and numbered keychains can be seen in the office throughout the movie.  There are 12 rooms and 12 keychains. 

The Secret Life of Walter Mitty

Walter Mitty (Ben Stiller) is renting a car in Iceland.  They only have two which is shown first by the fact the rental agent only has two keys on his key rack.  They have the basic plastic white keychains attached.  (this was taken from the trailer for the movie)

Men in Black

Tommy Lee Jones' character K has a unique metal cone keychain.  It looks like a carpenters plumb.

Equilibrium

Christian Bale's character is out in the "nether" (outside the city walls) trying to hide a puppy in his trunk.  His keychain is a blank (probably) silver oval and a long metal rod.  It matches his character who is supposed to be completely emotionless. 

Duplicity

Clive Owen and Julia Roberts are corporate spies who use a rubik's cube keychain to signal each other.

Dylan Dog: Dead of Night

Dylan is being driven by his newly zombified best friend; his white rabbit's foot keychain can be seen in the ignition.  (The box if filled with wooden tipped bullets to fight vampires.)

Twins

Arnold Schwarzenegger is looking for his brother Danny Devito in Houston.  He steals a cowboy's car (only temporarily). The man left his keys and very appropriate six shooter keychain in the ignition.

The Cleveland Show

Holt looses his car at a crooked river boat casino after symbolically betting his keys and steering wheel keychain.  The tic tac toe playing chicken takes his keys off the table.

The Apartment

I do not believe there is a keychain featured in this 1960 comedy BUT the poster has one prominently displayed.

Wonder Woman-DC Nation Short

In  this highly stylized animated short Wonder Woman is saving Steve Trevors from the other Amazons.  Her 70's styled muscle car has a distinct eagle keychain hanging from the steering column. 

The short is from "DC Nation" a series of shorts appearing on cartoon network featuring various superheroes.  This is from 2 of 3 for this little set.  It can be seen here: http://www.youtube.com/watch?v=sA-cQf2Gfpw

National Treasure: Book of Secrets

Riley (Nick Cage's partner) spends all his money he made off of the first national treasure they found, partly on a ferrari.  He finds that he cannot pay his taxes and his car is seized.  At the end of the movie they find the treasure and he receives his car back from the government as a thank you.  He finds the keys with signature ferrari keychain in the envelope with the letter of thanks.

The Last of Us

In the video game The Last of US the main character Ellie always wears a backpack which has a cute purple monster keychain attached to a zipper.  Since it is part of the character design it can be seen throughout the game.

Christine

Based on the novel by Stephen King the movie features a murderous car.  The keys that went to the car had a Victor plastic teardrop keychain.

Kill Bill Vol. 1

Uma Thurman plays the protagonist who after waking from a coma begins a quest for vengeance starting with those who abused her while she was in the coma.  She takes her revenge and her abuser's car which perfectly matches his keychain. 

White Collar (Front Man)

The main character Neil is trying to convince a receptionist to give him sensitive information.  He sees her vanity name plate keychain and calls her by her first name, "Kathy", to get into her good graces.

Johnny Test

In this kid's cartoon Johnny has two genius sisters who create wild inventions.  In this episode they create a key that can open any lock.  And the keychain attached to that key is a red x.

Cloud Atlas

At a hotel where one of Tom Hanks' characters is the clerk the rack of room keys can be seen.  The keychains appear to be wooden knobs.

The Next Three Days

Russell Crowe's chracter tries to break his wife out of prison.  While going through the metal detector at the prison his Saint Christopher keychain is placed in the bowl.