Recurring theme:

Main character is a writer

Salem's Lot

Ben Mears is a successful author who decides to return home to Salem's Lot to write a book about a haunted house there.

It

Bill Denbrough grows up to be an author.

The Dark Half

Thad Beaumont is a successful writer who publishes his more gritty/racy novels under the pen name George Stark.

Bag of Bones

Mike Noonan is an author and former reporter who suffers from writers' block after his wife's death.

Cell

Clay Riddell is a struggling writer who has just lucked into a graphic novel deal when The Pulse is triggered and everyone around him turns into bloodthirsty maniacs.

Lisey's Story

Scott Landon is perhaps the most similar character to Stephen King (even more so than Thad Beaumont in The Dark Half). He writes a number of bestselling novels, wins the National Book Award and the Pulitzer Prize, and has a love for his wife which survives long after his death - in part, thanks to his writing.

The Stand

Harold Lauder, the 16 year old from Maine who likely has Asperger's, doesn't have any friends but finds an outlet in writing, writing strange stories in the 2nd POV and present tense.

Desperation

Johnny Marinville is a National Book Award winner and almost won the Nobel Prize for literature. Fun fact: his motorcycle tour across America is directly based on Stephen King's own tour, for Insomnia, in 1994.

Misery

Paul Sheldon is a popular romance novelist who tries to break into a more respectable genre.

Everything's Eventual

Richard Kinnell, the protagonist in The Road Virus Heads North, is a well known horror author.

The Green Mile

Paul Edgecombe isn't a professional writer, but painstakingly writes his memoirs.