I used to be a huge Stephen King mark, but then I reached adulthood. I still enjoy his short stories, because in reading them you get the sense that he's not pretending they're anything more than what they are - neat little comic book time-killers. His problem over the years is that he tends to regard everything he writes as precious, which directly contradicts all the writing advice from him that I've ever read. And now that he sleeps on a bed stuffed with $1000 bills, apparently there's no editor that he cannot overrule. Still, when he's on, he's on. When he's not using painfully outdated slang, or dwelling on the most uninteresting minutiae over multiple pages, or ripping his own characters off from earlier novels, or painting himself into a corner and half-assing an ending. Fifteen years ago or so, I'd say.
With all that said, here are the ones I still enjoy revisiting from time to time, in no particular order:
CHRISTINE - Don't laugh. If you read it with the spirit in which it was written in mind (A 1950s teen rebel movie mixed with EC horror comics), it's a great read. He has a really good insight into what makes a friendship a lifelong friendship here, and even though the premise of a killer car is inherently cheesy, there are some genuinely touching moments throughout. I even liked the way the narrative perspective shifts during the book. And they really should have included the rotting corpse of Roland Lebay driving the car in the movie. I read somewhere that Carpenter regrets not doing that. And the novel has a decent ending.
SALEM'S LOT - Everyone points to his description of small towns as a strong suit in this novel, but I think that's kind of horseshit. Almost every character is a douchebag deserving of being drained by the vampires, and in my opinion it's a very nihilistic, mean-spirited, short-sighted take on small town life - exactly the kind of thing an immature author who thinks he's got it all figured out would write. What works for me is King's attention to detail, the little bits of vampire lore and legend he incorporates into the story, and a truly suspenseful atmosphere - this underlying sense of dread you get all the way through the book, even during thee quieter parts. And, possibly because everyone else is such a shitheel, really likeable main protagonists, whom he's not afraid to harm (no spoilers).
PET SEMATARY - If there's one thing King truly does have an uncanny grasp on, it's the way older people think, act, and speak. Jud Crandall is pretty much my grandfather, and that's a large part of why I like the novel. Growing up in North Carolina, I got to here a lot of the old ghost stories like the Joe Baldwin legend or the one about the Devil's Hoofprints, and I also read all the "Ghosts of the Carolinas" books with their faked ghost pictures. The flashback stories about the cemetery's history reminded me a lot of those tales. And, in my opinion it has the only truly great ending of all King's novels. King must have been doing mounds of coke when he wrote the screenplay, as he completely misses the point of his own novel. In the novel, not everyone buried in the cemetery comes back "evil" (although they are changed in significant ways), while in the movie everything comes back as a snarling ghoul. Why would anyone want to resurrect a living creature knowing from history that it would be this demonic undead thing which would try to kill them is beyond me, but in the book you can understand why someone would want to take a chance - in the book, there was the possibility that whatever you brought back to life might be almost normal.
MISERY - Skip the "romance novel" portions (they aren't necessary to the story, and they're dreadful), and this is a crackerjack suspense novel. A great, classic character in Annie Wilkes, one who'll lull you into letting your guard down with motherly attention, only to cut off your thumb when you complain about the space key on your fleamarket typewriter (the movie is good, but pussies out on a lot of stuff). It's got the flavor of one of King's crime or mystery stories to me, and I really enjoy his crime stuff (he could have been an excellent crime genre novelist, and still cranks out a decent crime thriller short story every now and then). The transition Paul Sheldon goes through, from being helpless invalid, to relying on Annie for his very life, to actively trying to extricate himself from a dire situation, is very well-handled.
There are a few others I can read through again, but these are the ones with a permanent space on the bookshelf.