Tough to argue against the the old classics like Casablanca, all the Hitchcocks (my favorite North By Northwest), Citizen Kane, et al making the GOAT list, they've all aged beautifully. The Godfather - a no brainer.
For comedy I'd rank Dr. Strangelove, Young Frankenstein, Casino Royale, Clue, Bringing Up Baby and Christmas Vacation as immortals.
For romance I'd rank A Good Year, Sleepless in Seattle and Moonstruck as classic bests.
For other genres I'd rank It's A Wonderful Life, Gone with the Wind, To Kill A Mockingbird, Green Card, Castaway, Pulp Fiction, Apocolypse Now and Hunt For Red October up for consideration.
Int'l considerations Farewell My Concubine, Slumdog Millionaire and The Virgin Spring (Ingmar Bergman)
Offbeat considerations The Swimmer (Burt Lancaster), Things To Do In Denver When You're Dead, True Romance, Blade Runner ?