The Dark Tower III: The Waste Lands (Aug 1991)

Part III of an epic saga. Roland and his companions, Eddie and Susannah Dean, find the Path of the Beam that will lead them to the Dark Tower. Along the way, Roland adds two new members to his ka-tet (a group united for a specific purpose). In the decaying city of Lud, they encounter new dangers, including a sentient train that has gone insane.

The Dark Tower III: The Waste Lands has connections to the following books:

Book 1 / Part I / Chapter 13 : Maturin

Roland recalls his memory of the twelve guardians of the beam, including a poem we've heard before, in It.

THE GUNSLINGER RESUMED: “At each of the twelve lesser portals the Great Old Ones set a Guardian. In my childhood I could have named them all in the rimes my nursemaid-and Hax the cook-taught to me ... but my childhood was long ago. There was the Bear, of course, and the Fish ... the Lion ... the Bat. And the Turtle—he was an important one ...” The gunslinger looked up into the starry sky, his brow creased in deep thought. Then an amazingly sunny smile broke across his features and he recited: “See the TURTLE of enormous girth! On his shell he holds the earth...

Book 1 / Part II / Chapter 13 : The Territories

Calvin Tower mentions The Territories (as in, Brooklyn?) while he's negotiating with Jake for the Charlie the Choo-Choo book.

“Seven bucks and it’s yours. Plus tax, of course. The riddle book you can have for free. Consider it my gift to a boy wise enough to saddle up and light out for the territories on the last real day of spring.”

Book 1 / Part II / Chapter 13 : Ed Deepneau

Aaron Deepneau, a cousin of Ed's, is a major player in the quest for the Dark Tower.

“Don’t hurry off, Jake. Now that you’re here, come on over to the counter and have a cup of coffee. Your eyes will widen with amazement as I cut Aaron Deepneau’s spavined old Kiev Defense to ribbons.”

Book 1 / Part III / Chapter 2 : Co-Op City

Eddie helps Jake get back to Roland.

“How will I find you? Jake was suddenly terrified that the boy would melt away completely before he could say everything Jake needed to hear. No problem, the boy said. His voice had taken on a queer, chiming echo. Just take the subway to Co-Op City. You’ll find me.”

Book 2 / Part V / Chapter 21 : Pennywise

Eddie and Susannah come across a damaged young man in Lud and note that he reminds them of, respectively, Ronald McDonald and Clarabell the Clown. In IT, George sees Pennywise in the drain and thinks that he looks like a cross between Bozo and Clarabell. King notes that if George had been alive a year later, he probably would have been more likely to relate him to Ronald McDonald.

Come on, you deucies!” a relatively young man snarled. He wore his blue scarf around his throat like a rally-racer’s ascot. He was bald except for two fluffs of frizzy red hair, one on each side of his head. To Susannah, this fellow looked like Clarabell the Clown; to Eddie he looked like Ronald McDonald; to both of them he looked like trouble: He threw a homemade spear that might have started life as a steel tableleg.

Book 2 / Part V / Chapter 40 : Randall Flagg

Flagg introduces himself with a typical RF alias, after Roland has known him as Walter O'Dim and Marten Broadclock at various points in his life.

“Call me Fannin,” the grinning apparition said. “Richard Fannin. That’s not exactly right, maybe, but I reckon it’s close enough for government work.” He held out a hand whose palm was utterly devoid of lines. “What do you say, pard? Shake the hand that shook the world.”

References will be here!