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.