The Onion A.V. Club's companion pieces Lost In Translation: 20 Good Books Made Into Not-So-Good Movies and If You Film It . . . 21 Good Books That Need To Be Great Films, Like Now are both worth reading.
John Kennedy Toole's A Confederacy of Dunces has been atop these sort of "why haven't they filmed this yet?!" lists for decades. If If I ran a major studio, Jonathan Franzen's The Corrections and John Updike's Rabbit Is Rich would be right alongside it at the top of my list.
Among the famously bad film adaptations, The Bonfires of the Vanities has got to be at the top of the list. Man, that was a terrible movie. Tom Hanks as the arrogant Master of the Universe investment banker? Bruce Willis as the wimpy, dandified British journalist? Morgan Freeman as the Yiddish-speaking Jewish judge? Fifteen years after the fact, its hard to believe that the movie ever actually happened. Both of the recent Dr. Suess adaptations were horrible, and now Jim Carrey, who butchered How the Grinch Stole Christmas, is about to sink his claws into Charles Dickens' A Christmas Carol, the greatest Christmas story ever written. Rumor has it that he has been cast as all of the following characters: Ebenezer Scrooge, The Ghost of Christmas Past, The Ghost of Christmas Present, and the Ghost of Christmas Yet To Come. Fortunately, Tom Hanks is being cast as Bob Cratchit and Bob Hoskins as Mr. Fezziwig, so there's hope for it yet. Michael J. Fox is supposed to play Tiny Tim, which (I devoutly hope) means the movie is animated.
What, though, of the great novels which become the basis of classic movies that have little to do with the original source material? The Shining and A River Runs Through It are two examples that come to mind immediately. Both movies feature classic performances, beautiful cinematography, iconic imagery . . . and plots that differ significantly from the original novels. Are these works of cinematic art co-equal with the source novels in prestige and literary value; the work of great directors and actors at the top of their craft? Or are these movies just crass examples of Hollywood poaching good ideas from more serious artists in their never-ending effort to appease crowds to unsophisticated to appreciate great fiction?