No particular order. Also, it’s movies that I watched, can’t speak on essentials that I might be missing.
It’s kinda hard to make a list on essentials tho. Because your personal taste obviously plays a big role. I can’t see my girlfriend liking more than 10 percent of those…
Schindlers List
Gladiator
No country for old men
The grand Budapest hotel
The big Lebowski
The Fellowship of the Ring, The Two Towers
Star Wars (the original one)
Requiem for a dream
Pulp fiction
The good, the bad, the ugly
The lives of others
La vita é Bella
All quiet on the western front (1930 version)
The dark knight
The Truman Show
2001: Space odyssey
Alien
7 Samurai
Princess Mononoke
Trainspotting
Boyz N the Hood
Scarface
The Godfather 1, 2
The Matrix
Clockwork Orange
Shutter Island
Kingdom of Heaven
Wolf of Wall Street
Honorable mentions because they are popular and everybody always talks about them (I like a lot of them, too. Don’t consider them essentials tho):
Inception
Interstellar
Fight Club
Harry Potter
Return of the King
Rest of Star Wars (whatever people consider the good ones at last)
Saving Private Ryan
Django Unchained
Toy Story
The Lion King