I'm gonna second AN INNOCENT MAN for the best of the bunch, Selleck's finest film IMHO. For a futuristic prison flick I'll take FORTRESS. I know it's only a small part of the film but the prison scenes in AMERICAN HISTORY X are, um, sort of hard to forget. If you want to see a prison flick with Willem Dafoe, Tom Arnold, and Mickey Rourke in drag there's always ANIMAL FACTORY, not great but probably worth something for its various oddities.