Ah man... this is a tricky one. I actually think books and shows had a much bigger impact on me than movies actually did, and that I write more like a comics or TV writer than a movie writer. Let's see... (sorry in advance, I can't be bothered to look up the date of all these movies)...
Star Wars: A New Hope - I just think this is about as close to a perfect movie as has ever been made. It's so simple and captivating. The clarity of storytelling, the use of simple themes and archetypes... and yet with a setting and concepts that would have been so alien at the time. It's a perfect example of really good execution of classic story tropes turning a complicated mix of pulp sci-fi, Westerns, Samurai movies and WW2 films into something almost anyone can enjoy. I think knowing that's how I feel about this film, and why I use it as my go-to example for explaining the mechanics of storytelling, says a lot about me.
Wallace and Gromit: The Wrong Trousers - It's a short film at just around the length of a TV episode, but still a film (it won an Oscar and everything!), and it feels like a film because it packs so much in. The Wrong Trousers perfectly blends understated Northern English humour, Hichcock-inspired drama and amazing action sequences, like the model train chase sequence, which is just perfection to me.
The Incredibles - Watching this with the commentary on taught me so much about how to structure and storyboard a story. Brad Bird may not really be the nicest person, but he is very, very good at constructing emotional stories told very clearly and with attention to detail (and was hugely influential in use of that formula in The Simpsons early on). The Iron Giant is similarly great, but The Incredibles is the one I've watched a ton of times, so makes it onto this list.
Glass Onion - God, I just love this movie. You can re-watch this movie and see all the clues right there in plain sight, the interplay of cleverness and simplicity disguised as cleverness, and cleverness that seems like simplicity is incredible. The way it uses visual storytelling and small details it throws in, even down to the wardrobe, to help flesh out a large cast and make them all feel well-realised.
Enter the Spider-Verse - This is a fun movie with a great heart that nails not just natural feeling speaking dialogue, but larger-than life cartoon characters. Everyone has so much personality, and the humour is great. I also really like how it exhaustively explores deep themes, like parenthood and expectations, while also being a fun romp on the surface.
Legally Blonde - Not because this movie influenced me especially, but because it perfectly uses the beats of Save the Cat, both exactly to the letter, and yet not in the most boring, uninspired way, and if you're looking to understand how I write, understanding that I value using carefully constructed structures and then bending an unusual narrative to fit them will get you a long way.
Four Weddings and a Funeral - This was my older sister's favourite movie when I was a kid and she was a teenager and she watched it over and over, so I basically have the whole thing burned into my brain. I think the style of the comedy and dialogue did influence me... or maybe just Richard Curtis in general since he was everywhere in British comedy back then.
Emma (1996) - Speaking of things my older sister watched a lot! Jane Austen adaptations! Especially this one! I think that even though they're very old, there's still something very "true" in Austen's work about the nature of romance and relationships. Austen writes romance like a battle of wits or a tense negotiation, and I love when film adaptations get that and really make you feel that tension. Everyone's fully clothed and acting very proper, but they're all about to explode.
Tangled - Until Encanto, this was my favourite Disney film. I still think in a lot of ways this is the most "me" Disney film. I just find the choice to make the villain a narcissistic and controlling abusive parent figure, and so to make a large part of the heroine's story recognising and overcoming the trauma that's left her with, making it as much an internal struggle as an external one is fascinating and fresh.
Final Fantasy VII Advent Children - This is not a particularly good movie, but I watched it a ton in Uni because I was just desperate for a movie with this sort of... overblown, dreamlike, anime feeling. In FF7:AC it's like the laws of physics are based on "what would be cool?" Or "What do you feel like you ought to be able to do?" It's simple, big melodrama and the power of friendship allowing a group of people to basically do the D&D "Peasant Railgun" meme to fling a guy into the sky.
Scott Pilgrim vs The World - This is almost a cheat entry because it's really the comics that influenced me. I read the comics first, I was a huge fan of the comics and while I enjoy this movie, I don't think it does the depth of the plot or especially characterisation of the comics justice. All that said, the movie does capture the snappiness of the dialogue and humour of the comic, as well as the use of anime and game tropes as metaphors for mundane, real life stuff.
Shaun of the Dead - Speaking of Edgar Wright.... This is such a smart movie. It's interesting as a coming-of-age story about characters who are a bit older, but are more like metaphorical children. I love using Fantasy to explore mundane human experiences, and this one does it so well. It's the most perfect execution of a weird British show like Black Books or Spaced (it even has most of the same cast as Spaced and the same creator) turned into a movie with movie stakes and pacing. Also this is the only zombie movie with a realistic ending where the army are competent, which makes my pedantic brain happy! 
The Heat - Not necessarily a great movie BUT! The fact that this is one of my favourite movies says a lot about me. If you've never seen The Heat, it's a Buddy Cop movie where Melissa McCarthy plays a working class beat cop who plays fast and loose with the rules, and Sandra Bullock plays a highly ambitious FBI agent who really wants to be the cool boss guy, but alienates everyone because she's incredibly abrasive and uncharismatic... and then they have to team up. The awkwardness of these loser characters bumbling their way through everything... the way it addresses on a meta-level how a woman, or a female character with exactly the same traits as a male one who'd be seen as cool, gets perceived as "annoying" or "unlikeable" and they have to be brought low and humiliated to be accepted... This is just such an interesting piece of media.
Whew, I did it! Thirteen!
