8. Frances McDormand and Holly Hunter
These costars in 1987 comedy Raising Arizona go back to McDormand's grad school days. They met through their boyfriends who were best friends, and when the couples split up, the ladies moved in as Bronx roommates together! Later, after McDormand met and married Joel Coen, they lived with Hunter for a while and director Sam Raimi, which led to Coen later writing a role just for Hunter in Raising Arizona.