Imagine if you will for a moment these following films that never saw the light of day.
Stanley Kubrick's Childhood's End
Philip Kaufman's Star Trek: Planet of the Titans
Kevin Smith's Six Million Dollar Man
Tim Burton's Superman Lives
James Cameron's Spider-Man
Terry Gilliam's Watchmen
Ridley Scott's I Am Legend
I would pay money to see any of them. But this book details why I can't see them, as well as looking at the troubled creation of some films that did get made like Dune and Alien3.