Ethan Hawke - The Hottest State
They’re made-for-TV, but Colin Dexter made a cameo appearance in (I believe) every one of the Inspector Morse mysteries based on his novels.
Didn’t Howards Stern not only star in Private Parts but also write the book?
I’m not sure on this one though.
Henry Miller appears in the film version of Tropic of Cancer and Paul Bowles is in The Sheltering Sky.
Hal Holbrook starred in Mark Twain Tonight, based on an adaptation of Twain’s writings that he put together for the stage.
Jacqueline Susann had small cameos in the movies of her novels Valley of the Dolls and The Love Machine.
The IMDb lists Mark Twain (!) as an actor in two adaptations, but I’m not sure if it’s to be trusted.
Jean Shepherd narrates, and has a cameo, in A Christmas Story.
SE Hinton was in The Outsiders (as a nurse, IIRC.)
Chaim Potok has a cameo as a Talmud scholar in The Chosen.
In Everybody’s All-American, Frank Deford has one line as the owner of a diner.
King played the title role in the Creepshow segment, "The Lonesome Death of Jordy Verril".
Jordy Verrill: Meteor shit!
That was pretty good acting from King
Armistead Maupin did a cameo in the wonderful made-for-TV production of Tales of the City.
Terry Pratchett played The Toymaker in the *Hogfather * movie
He’s also going to be in The Colour Of Magic movie, in production
Leslie Chateris was an extra in an episode of The Saint
Frank Miller was the priest in Sin City
There is, by the way, a popular legend that Ian Fleming was an extra in one of the early Bond movies. This story is not true, based upon mistaken identification. An extra in a scene wore a particular type of jacket, Ian Fleming was photographed on set wearing a similar jacket.
Charles Bukowski was a barfly in the movie Barfly.
Tama Janowitz had a brief cameo in Slaves of New York.
Joseph Wambaugh’s The Blue Knight was made into a TV movie, and he had a small role in that.
He also had a blink-and-you-miss-it part in Daredevil as “Man with pen in head”.
He was also the man running naked into the ocean in the BBC series version.
/hijack - biographical movies in which title character plays another role/ Erin Brockovich plays a waitress in that movie.