Stephen King recently discussed this very subject with Entertainment Weekly.
He lists the following connections, though, some are tenuous at best:
The Shining and Doctor Sleep
Psychic powers in The Dark Tower film are referred to as “The Shine,” which means Jake Chambers, the boy at the center of the story, has the same abilities that Danny Torrance had in King’s classic 1977 novel (and the 2013 sequel Doctor Sleep). Is the Shine becoming his catch-all psychic ability? Does that mean the wallflower-turned-prom-queen in Carrie had a malevolent version of The Shine? “I don’t know, man,” King says with a laugh. “It’s like the guy says in House of Cards: ‘You might think so, but I couldn’t possibly comment.’”
The Stand and Eyes of the Dragon
Randall Flagg, the sharp-tongued, charismatic villain from King’s 1979 Americana apocalypse and his 1987 old-school fairy tale, is the same sinister presence Matthew McConaughey plays in The Dark Tower, only operating a different alias – Walter, The Man in Black. “At some point I realized that Randall Flagg and Walter were the same character and once you take this whole idea in mind that Mid-World is connected to our world you say, ‘Well okay, this guy shows up again and again,’” King says. Did he just like seeing this devil again? King shudders: “I never want to see that guy.”
Hearts in Atlantis
In the 1999 story collection, Ted Brautigan is a psychic who, like Jake in the movie, is being pursued as a “Breaker,” someone whose power can help collapse the Tower. The 2001 movie dropped the Tower references, and instead had the Anthony Hopkins character being pursued by government agents for clandestine Cold War research. “I wish they had gone more supernatural with that,” King says of the movie. “I thought there was a way to do that without feeding into the whole Dark Tower thing.”
In the film version of The Dark Tower, there’s an older Breaker who is somewhat inspired by Ted Brautigan, although it’s not the same character. Director and co-writer Nikolaj Arcel said he wanted someone who was older than Jake, someone who had been enslaved by the Man in Black for a long time. So there’ll be flashes back to this figure’s younger days – in the way-back era of the 1990s.
In this 1975 book, the fallen priest who loses his faith and drinks the blood of a vampire later becomes a key ally of Roland the Gunslinger in the latter Dark Tower books. If there are sequels to the movie, it’s possible he may turn up onscreen. “Father Callahan…” King says wistfully. “I’d love to see him in there. But we’ll have to see how the [first] film does.”
An elderly man who begins having visions after losing the ability to sleep comes to learn about a mystical tower that stands for all the levels of reality – and the agents of the Crimson King who wishes to tear it down. Before this 1994 novel, the Tower saga was separate from King’s other novels. “Insomnia was the first place where I really understood [the links] consciously and I started to work all this stuff in there,” the author says.
The Talisman and Black House
These fantasy epics, co-written with Peter Straub, take place in The Territories, a neighbor to The Dark Tower’s Mid-World. The connection wasn’t made in 1984’s The Talisman, but for the 2001 sequel, King and Straub tied them together explicitly. “It seemed to me almost undeniable, and it did to Peter, too, that if we were talking about another world you could flip into, it would be related to Mid-World,” King says, referencing similar adjacent realms from Game of Thrones. “An analog would be Westeros and Meereen.”
In the midst of our conversation, King drops a bombshell: There’s a third Talisman books in the works. At least, it’s currently germinating in his and Straub’s heads. “Peter and I have started to talk about the third book in the cycle, so you know, we’ll see what happens, whether or not that’s there,” King says. “I think that he’s got some great ideas.”
Later in The Dark Tower books, Roland and his posse meet Dandelo, a creature who feeds on emotion, just like the fiend that manifested itself as Pennywise the Clown. Fans theorize they’re the same kind of monster, but King doesn’t go that far. “I would say that they were probably related just because they both came from my head,” he says. “But it wasn’t a conscious thing to say one was like the other.”
“The Jaunt” (collected in Skeleton Crew)
In The Dark Tower, some portals between worlds are technologically created, so producers of the movie asked King if they should follow the rules established by this 1981 short story. It’s about a mass-transit system that opens time/space portals, but if passengers go through awake they emerge insane on the other side. King’s response: Laughter. “If you’re mind’s going there, go with God,” he says. “I feel like that with most of this stuff.”
For a more in-depth list of connections, one can look to King's own website, which adds a number of other minor connections.