Recently the movie The Frinds of Eddie Coyle came out on DVD and probably got at least a few people interested in the Georges V. Higgins novel it's based on.
I also recently saw the movie Straight Time (a very miscast Dustin Hoffman) and I've gone looking for the book of the same name it's based on by Edward Bunker (who has a cameo in the movie) and I've been looking for the novel that the Jack Lemmon movie, Save the Tiger was based on.
These are what I'd call "odd category" books as they aren't really mysteries and not exactly pulp.
So, I was wondering, what other older books would you put in this category?