Almost no DMs can claim they've NEVER stolen a plot, for a session or a full campaign, from their favorite piece of media, be it a show, movie, book, video game, or anything else. I want to make a huge resource of stuff prospective DMs can look to for inspiration. What I'm putting here is stuff that i've both used and am planning to use :)

- Infinity Train: If you run sort of funky campaigns with quirky NPCs, this show is a GOLD MINE. I've used "Kick This Frog" in a dungeon before and it's absolutely incredible. The show centers on a train where each car contains a different environment, often with a puzzle, either physical or social, involved. They're perfect for quick puzzles and roleplay moments, or setups for much bigger things.

- Stranger Things: This one's a little basic, sure, but really what i took most from this show was visualizations in my mind's eye for creepy stuff, which really augmented my descriptions. The rift to the abyss in my last campaign was gross, and i used oozes and dungeon obstacles from the DMG to match the vision i was looking for, and it worked amazingly.

- Discworld: Terry Pratchett's absurdly long book series. The incredibly loose magic system in this series, as well as the mannerisms and absurdity of its characters, are constantly pulled into my worlds. Loosely defined magic systems aren't something you'd think would work in a game with a magic system so clearly delineated, but figuring out what arcanobabble you can use to explain away the random stuff you want magic to do in your campaign is great for making the world feel more your own, and the system of consequences for magic in these books are also really fun to add, not as new rules, but for special occasions. As for the characters, if you know both this series and Infinity Train you may be able to sense a theme, but basically i'm a sucker for fantasy that takes fantasy to its weirdest corners and flips its stereotypes in a way that makes the setting feel less uniform. 

There are some episodic shows, where an individual episode can be a setup for a oneshot or side quest. Some i might pull from in the future are:

-  Doctor Who: I mean OBVIOUSLY. Take out the time travel (or don't, I don't control you,) and you've got free weird monsters, red herrings, funky settings, and possibly new long standing NPCs depending on how you set it up. Often the episodes don't tend to end with FIGHTING the monster, so if that's what you’re going for, you could either change up the plot a little or just... not use it.

- Buffy the Vampire Slayer: This one might take a little more reconfiguring, but if you strip the episodes down to their bare plots, you could take any one-off villain and turn them into the BBEG of your campaign, because Buffy is not a show that particularly cares about the consistency of the power levels in its villains from one episode to the next. This show is CERTAINLY one that ends with a big fight with the bad guy almost every time, plus the characters are so colorful that any one of them that you decide to transport into your campaign will almost certainly become a party favorite.

So, what stuff do you pray no one in your party has watched so that you may contort it into your own beautiful creation?

to whom it may concern: please let there be a spelljammer supplement and please let it include space lobsters. my totally original and not at all plagiarized crew of burgeoning long distance delivery adventurers feel that claws for hands would come in handy for the open ship's healer position. make this easy for me, please. thanks.

(ps: and maybe whalers on a moon. they'd carry a harpoon. but if there ain't no whales, then they'd tell tall tales and sing a whaling tune.)

...more closely related to the original poster's premise, just within the last day i've recommended cribbing the volcano lair from the Incredibles movie, betrayal from the Solo movie, and the orange juice numbers heist from the 80's movie Trading Places. for me it's less that i hope no one will notice where i've taken my inspiration and more that i hope it hits them like a ton of bricks after they're already deep, deep into it. :D

I recently watched an anime called Heaven's Official Blessing that had two monster-hunting arcs (one in an abandoned mountain temple, one in a desert ghost town) that were perfect for dropping into a campaign. They had random encounters and NPC quest givers and everything!

I've mentioned before, speaking of Doctor Who, how I lifted basically the whole plot of Mummy on the Orient Express in an Ebberon campaign. Also how I like to "borrow" lore from 1999 jrpg (and belive it or not, NOT a FF7 ripoff as they were in production around the same time) Legend of Dragoon, which has this cool expansive world chock-full of fun ideas and unique elements (if I ever need to run Mechanus, I'll definitely have it work like the ancient Law city of Zenebatos), and interesting characters to take inspiration from. 

Recently I wrote an encounter for a one-off combat inspired (read: stolen) from the X-Men villain Danger, where an ally of the party invents a magical simulation the party can use to train to fight the big bad with, only of the machine to gain sentience and wrestle with its programming directive to try and kill the party vs its programmed failsafe to keep it from killing anyone, so it tries killing the party through less conventional means while warping the battlefield and trapping them in the simulation until they escape. That was fun. 

I'm also currently writing an adventure inspired, of all places, by a Call of Duty Zombie level that took place on the Titanic. Now, I've never really been a fan of call of duty and frankly I'm pretty bored of zombies, but a while back I was hanging out with a friend who wanted to play it and while the game was meh, something about the setting and the pulpy characters appealed to me in a way that made me want to write my own take on the concept. Coupled with that being around when I discovered The Homebrewery, and now I'm putting it together hopefully to publish online once it's done! 

I definitely think inspiration is best drawn from a wide, unconscious, obscure net. Inspiration is best when your brain is just kind of taking all the references in your head and throwing them in a blender, sieving out bits and combining them with other bits in a way that re-makes them into something completely unique. 

Maybe not entire plots, but My Little Pony and True and the Rainbow Kingdom are both amazing sources for magic items, plot devices, cool creatures, effects, spells, characters etc. 

Like the Wishes from True or that weird omnipotent dragon from MLP. 

Yup, I have small children. 😂 I've gotten lots of ideas from these shows. Remarkably well written shows. 

I recall at some point the god-like MLP dragon actually created a DnD adventure illusion world and sent the characters there. 😅

The wishes from True are granted by the Tree based on their needs. So the tree predicts the future and grants three useful wishes, which are basically single use spell effects etc. True doesn't know why she was given such wishes, but they always turn out handy.

So, since the DM knows what the players will face, a Wish thing similar to the Tree could grant them a Water Breathing wish when they are entering a place with water. The players don't know what to expect, except now they think maybe water at some point? 

While I used the book for it specifically, I have used It as the basis for a few campaigns (my player's like it).

Had to develop entire sets of rules about being kids for it, lol.  Next version doesn't have them as kids, but revisists it later in the campaign.

My Campaign I am developing out right now for start of play next year uses all of the following as elements, often intermixed:

• It
• Blade
• The Shining
• Deliverance
• Smokey & The Bandit
• Knight & Day
• The 5 Element
• Mission Impossible
• No Country for Old Men
• Sleight
• Violet Evergarden
• Under the Tuscan Sun
• Casablanca
• The Incredibles
• Labyrinth
• Encanto
• The Craft
• Seven
• Cast a Deadly Spell
• Gangs of New York
• The Warriors
• The Godfather (inspo only)
• Wyatt Earp
• Fistful of Dollars
• Sons of Katie Elder
• The Big Sleep
• Ocean’s 8
• Thief
• Mr & Ms Smith
• Rescue the Princess
• The Losers
• The Princess Bride
• Akame ga Kill
• The Mummy & The Mummy Returns

I am likely to add additional ones in. There are 21 total adventures, but there are also a bunch of sidequests.

The Warriors.

I've said Samurai Jack before, but anything by Tartakovsky is a clinic on minimalist storytelling.

Memento: An excellent method of revision to the whole retrace-and-investigate trope imvho, without the monotony of being fully procedural such as your average cable network investigation shows or movies. I utilized portions of the movie to lead into and then thicken the general plot of Waterdeep: Dragonheist. I believe the best part was the look on the faces of the players when they realized everything they were tracing and investigating were, in fact, the crimes  being committed by them. Some with and some without their knowledge, lol.

I quickly followed that up with an version of The Count of Monte Cristo and it made for a most excellent follow-up campaign. The players were not expecting, again, to be on the receiving end of their own investigation, albeit chalked it up to petty vengeance so it lost steam toward the end. Sadface.

There are many more movies, shows, books, comics, etc. etc. that I've gleaned ideas from, but those two seemed to excite the players a bit more because of the mental intrigue without so much of the puzzles (they're fking horrible at puzzles...)