Suggestion
Just finished watching this movie on DVD, when I noticed there is a Director's commentary. He wrote the screenplay as well, so he gives a lot of insight into the film, including the changes from the book (including why he changed the ending and the author's opinion about it), why he shot it in black and white, original casting ideas (Haylie Mills as Selina!) etc.
This movie has always been one of my favorites and I loved finding out more about the "behind the scenes" of it. I highly recommend it to anyone who is interested in knowing more.