I can think of only a few:
Shakespeare’s Tragedy of Julius Cæsar was more a tragedy about Brutus **
The musical Gypsy actually focuses more on Mama Rose
Marvin’s Room- in the movie, Marvin is a non-speaking cameo by Hume Cronyn (as a multiple stroke victim) while in the play Marvin isn’t seen at all
It’s arguable whether the Fiddler on the Roof is a title character, but he is a character in the play (sort of) and is non-speaking and only in a couple of scenes.
Others?
Waiting for Godot would be the most extreme example.
The original Thin Man did not refer to Nick Charles, though the subsequent sequels applied the moniker to him.
Buster Keaton’s The General and The Navigator actually refer to vehicles; Keaton’s just the one who operates them.
In Rebecca, the title character only lives as a memory in the story.
The Three Musketeers is really D’Artagnan’s tale.
Natty Bumppo was not The Last of the Mohicans.
Dorothy Gale is the lead of The Wizard of Oz.
Pasolini’s The Gospel According to St. Matthew is about Jesus.
The Bride of Frankenstein only appears at the end of the film.
I think it’s safe to say Margo Channing is the lead character in All About Eve.
Chasing Amy Amy never even appears and is only even mentioned by one minor character in one brief scene. Probably on par with “Waiting for Godot” for extremity.
Lord of the Rings Sauron ‘appears’ in only a couple of paragraphs in the book and just a few brief seconds of some 6 hours of movies.
Saving Private Ryan Ryan is essentially a minor character and gets less screen time than any other member of the squad.
Um. Bill only has a single line of dialogue (and is never really seen) in Kill Bill Vol. 1
Luckily for everyone, Tom Cruise is not The Last Samurai (or is he?)
Just thought of another one:
Oliver Stone’s JFK
The Third Man only really appears at the end of the film.
Didn’t Harry Lime appear more like at the halfway point?
Howz about:
A Fish Called Wanda
Searching for Bobby Fischer
Roger and Me
Being John Malkovich
Perhaps the most famous literary take on this idea is David Copperfield. He is the narrator of the book but he wonders whether he will turn out to be the “hero” of his own life, or will it be Steerforth.
The movie ** Laura** is actually an investigation into her supposed murder. A faceless corpse is discovered and presumed by everyone, including the police to be her. A great movie, but I always wondered didn’t anybody ever fingerprint the corpse.
All the President’s Men is not about any of them but rather about the reporters investigating them.
All the King’d Men is about the King, Huey Long, and not his men at all.
Dracula, both the Bela Lugosi movie and Stoker’s novel, are not (or at best only tangentially) about Dracula. The real story revolves around the vampire hunters and those whose lives are destroyed by the vampire.
I’m sure there are a lot more examples. These are the one’s that occur to me at the moment.
I’m having a mental debate about whether this applies to The Great Gatsby.
Well, I would say that Douglas Adams’ “Dirk Gently’s holistic detective agency” wasn’t really about Dirk. (Technically the agency is the actual title, but I think we can be flexible enough to not worry about that, since Dirk’s whole name appears in the title and is the commonly given short-name of the book.)
Certainly Dirk serves as a major character in the book, and he’s the sleuth who, after a fashion, solves the mystery, but he isn’t more important than some of the other characters, and we never get shown, directly, what he’s thinking, as is true of Richard, and Gordon, and even the Monk. Personally, I’d say that Richard is the main protagonist of the book, but maybe that’s just because I identify with him so strongly. 
Any counter-points out there?? (Oddly enough, in the one and a half sequels Dirk really comes into his own as a main character.)
I think *Othello * is really Iago’s play.
It’s going to become an extremely long and easily-added-to list if we say that DGHDA counts. After all Dirk appears in or is mentioned in pretty much every scene in that book from the first to the last. He interacts with every single character as far as i recall and his character (not just his existence) is solely responsible for moving the plot along and his character evolves as much as any other character. We know approximately as much about Dirk’s actions and intentions within the story as we know about the other characters.
That differs form the other examples where the title character doesn’t even appear in numerous key scenes or is even dead or missing when the scenes occur. The deliberate actions of those characters have little effect on the course of much of the story. Andof ocurse we don’t actually get to know as much about most of those characters, even Caesar, as we do about the real hero.
If we include DGHDA then we need to include almost every story that isn’t essentially a one-person ‘biography’ like “Forrest Gump”. So throw in all Sherlock Holmes (they primarily focus on Waston and the ‘victims’), throw in Return of the King (we never know Aragorn’s thoughts either and he is certainly secondary to Frodo and even Gandalf). Add even throw in “Return of the Jedi”.
While Dirk and Aragorn and Luke may not be “the” main protagonists of their stories they are certainly major characters in the unfolding story. There’s going to be some argument about when a characeter ceases to be major of course, but I think that any character that appears in or is directly instrumental in setting up (or failing to prevent) every major scene in a story is major. And any charcter that gets apporoximately equal “screen time” as the other also should count IMO.
In that respect we could also add The Lion, The Witch and the Wardrobe where the children are obviously the “heroes” and the lion and witch don’t have much showing . Also Moby Dick since the whale really serves only as foil/goal, not a character per se.
The Rocky Horror Picture Show seems to me to focus on those 2 Earth twits Brad Majors (Asshole!) and Janet Weiss (Slut!) Rocky does show but has no speaking lines.
Neuromancer was the first that came to me.
To Wong Foo, Thanks for Everyting, Julie Newmar. Neither of them are in the film.
Similarly, in The Adventures of Priscilla, Queen of the Desert, Priscilla isn’t a charater; she’s a vehicle.
Raising Arizona – Arizona is the McGuffin, not the main character.
Eating Raoul – Raoul is eaten quite early on; it’s really about the Blands.
Glengarry Glen Ross – There is no one in the movie by that name. It comes from various names for housing developments (Glengarry Acres, Glen Ross Farms) used in the play, but there is no “Glengarry Glen Ross” ever mentioned.
Howards End – There is no Howard. It’s the name of a piece of property.
Waiting for Guffman – Guffman doesn’t appear.