I have a huge list of movies I could watch any time. It’s not that I’m constantly watching them, but if they happen to be on when I'm looking for something, I’ll definitely pick them. I'll use your format to lay mine out.
50s: North by Northwest, Vertigo, Rear Window (honestly, it’s easier just to say "all the Hitchcock films from the 50s"), 12 Angry Men, On the Waterfront, Ben-Hur, Rio Bravo, The Searchers, Sunset Blvd, Quo Vadis, Paths of Glory
60s: The Great Escape, Dr. Strangelove, Easy Rider, The Good, the Bad and the Ugly, Planet of the Apes, The Pink Panther, Psycho, The Italian Job, James Bond: Goldfinger, Night of the Living Dead, Black Sabbath
70s: Star Wars IV, The Godfather 1 and 2, Rocky 1 and 2, The Sting, Halloween, TCM, Dawn of the Dead, Alien, Jaws, The French Connection, One Flew Over the Cuckoo's Nest, The Driver
80s: Blade Runner, Star Wars V, The Terminator, Predator, Aliens, Die Hard, A Christmas Carol, Thief, Ghostbusters 1 and 2, Back to the Future 1 and 2, Indiana Jones 1, 2, and 3, Coming to America, Planes, Trains & Automobiles, The Breakfast Club, National Lampoon's Vacation, European Vacation, Christmas Vacation, Ferris Bueller's Day Off, Fast Times at Ridgemont High, The Thing, Day of the Dead, Escape from New York, Just Before Dawn, Burning, Scarface, Platoon. I should probably stop there—if I kept going with the 80s, I could spend all day listing comedies and horror flicks. For me, this was easily the best era.
90s: Reservoir Dogs, Pulp Fiction, Jurassic Park, Dumb and Dumber, Ace Ventura: Pet Detective, Home Alone 1 and 2, Ed Wood, The Usual Suspects, The Sixth Sense, Saving Private Ryan, The Shawshank Redemption, Forrest Gump, The Big Lebowski, Fargo, Seven, Scream 1 and 2, I Know What You Did Last Summer, The Kingpin. Same thing as the 80s, I could go on forever with this decade.
2000s: Big Fish, Lord of the Rings, Mulholland Drive, Batman Begins, The Prestige, The Dark Knight, No Country for Old Men, Kill Bill Vol. 1 & 2, [REC] 1 and 2, 28 Days Later, The Collector, Pineapple Express, Superbad, Borat, Jackass, etc.
2010s: The Conjuring, Baby Driver, Arrival, The Martian, Interstellar, Django Unchained, Blade Runner 2049, 50/50... there are definitely more.
I've seen every single one of these several times, but my absolute favorites have to be Star Wars, Pulp Fiction, Jaws, and Dawn of the Dead.