10. Harry Potter and the Prisoner of Azkaban

Say what you will—I do feel like a schmuck for putting this here, because I'm well-aware that the Harry Potter films aren't exactly masterpieces, and that they're kind of childish. But I don't really care—these movies take me back to a much happier time, when life was still fun, exciting, magical, and mysterious. But from a technical and narrative standpoint, Prisoner of Azkaban is probably the best one.
The franchise is well-renowned for its robust characters and strong performances, and Prisoner of Azkaban swings with the best of them—Daniel Radcliffe gives what is probably his most inspired performance in the series, which, of course, is supported by a bevy of other splendid actors, such as Gary Oldman, David Thewlis, and Alan Rickman (RIP).
It also has the coolest utilization of time travel in all of fiction (which is later fucking ruined by the Cursed Child), where everything that occurs takes place in a deterministic, self-fulfilling loop—which lends itself to many, many clever little narrative tricks and details for those who are paying attention.
Alfonso Cuaron's virtuosic direction is on full display here; there are some beautiful, beautiful shots in this movie, plenty of which contain some stunning imagery that I'll never forget.

9. The Dark Knight

This is the last guilty pleasure on my list. Though indisputably overrated, this is, without a doubt, the best superhero movie of all time, and the only one that's ever transcended the dreaded "capeshit" label. It's a genuine, bona fide, thematically-layered film that can actually be taken seriously AS a film—although, perhaps less so, because of all the memes. But at least the memes haven't mangled the film to the point where you can't take it seriously whatsoever.
I've heard some people say that Heath Ledger's Joker carries the whole movie, but I don't think that's fair to say. Sure, it's the greatest portrayal of the Joker of all time. Everybody knows that. But that doesn't mean he's all the movie has to offer. What if I said that Darth Vader carries Empire? People would go insane.
I actually honestly prefer Two-face. I find the tragedy surrounding his character a lot more interesting, and his moral compass resonates with me a lot. Aaron Eckhart also gives the performance of his life, but he's overshadowed so hard by Mr. J in this movie that I think a lot of people don't give him enough credit.
There's nothing more I can say about this movie that hasn't been said too often already, so I'll leave it there.
8. Reservoir Dogs

Hands down, Quentin Tarantino's best movie. He's yet to top it.
Acting, characters, cinematography, dialogue, narrative structure, themes—everything about this movie appeals to me so much, it's almost as though it was made specifically for me. It's so quotable—every single character has their own scumbag view of life, and the dialogue is so sharp and witty that, in the deepest recesses of your mind, you can't help but agree with some of the things they're saying about society (Mr. Pink's rant about tipping comes to mind).
It's a classic, simple movie that never cease to be entertaining. Out of all the movies on this list, I've probably seen this one the most often. It's definitely one of the most "watchable."
7. The Deer Hunter

Most of you probably haven't seen this one, but if you're into war movies, it's definitely a must-see. Not only is this the best Vietnam war movie; it's probably the best war movie period. Apocalypse Now and All Quiet on the Western Front come close, but it blows Full Meme-l Jacket out of the fucking water.
Robert de Niro is fucking awesome, and Christopher Walken gives the best performance in his career.
It's a slowburner; three hours long, and requires a lot of patience, but it pays off big time. It's well-known for having a few extremely tense Russian roulette scenes. That's all I really want to say about it, assuming you haven't already seen it. Go watch it.
6. Trainspotting

Mordo already discussed what makes this movie great, so I don't want to echo them here.
5. The Godfather

No explanation needed.
4. Stand By Me

Based on Stephen King's
The Body (a book I'm still yet to read), this is the first R-rated movie I've ever seen, and the first one I've ever called my "personal favorite." It's been surpassed by several films now, but it still holds a special place in my heart—and in the #4 spot.
This movie is my essence. It is the quintessential coming-of-age story—a subgenre that I'm quite fond of, having only recently gone over that hump myself. I identify with our four lead boys in so many different ways; no movie has better captured the essence of what it's like to grow out of your childhood. The acting is so real.
Some may find its misty-eyed sentimentality to be a little trite and hard to bear, but I think that's sort of half the point, because that's pretty much how kids are—especially when they're growing up.
This movie has sort of become a classic over the years, so if you haven't seen it already, shame on you.
3. Goodfellas

Mordo saves me another explanation. It may not be my favorite movie, but it's goddamn close. Scorsese is a god.
2. Requiem for a Dream

What's that?
A movie directed by Darren Aronofsky themed around the dangers of addiction that mercilessly beats you over the head with a "don't do drugs" message until you're too emotionally shaken to fall asleep because of how depressed the movie made you?
SIGN ME THE FUCK UPCouple that with Aronofsky's breathtakingly clever editing, Clint Mansell's excellent score (if you're capable of taking Lux Aeterna seriously), and excellent performances by the entire cast—special mentions to Ellen Burstyn and Jennifer Connelly—and you have one of my favorite movies of all time.
1. Fight Club

No surprises here.
By no means is this the greatest movie of all time—it's just my personal favorite, and perhaps always will be. It just resonates with me to my core, and it's often the first movie I ever recommend to people if they haven't already seen it.
The convenient thing about this movie is that anyone can like it, yet that doesn't dilute its quality any.
It's so stylish, and anti-corporate themes give me a massive boner. This is the movie that solidified David Fincher as my favorite director. He hasn't made anything that wasn't fantastic (Alien 3 doesn't count).
And that's my (super tentative and slightly rushed) list.
Honorable mentions: The Goonies, Scarface