Happened to pick up a book the other day called, "The Making of Casablanca." It's a new edition of a book originally published in 1992 entitled "Round up the Usual Suspects."
I'm in the middle of reading it and am finding it immensley enjoyable. It is richly researched, well-written and extremely interesting. Lots of technical details about the movie, the stars, how certain scenes came to be, etc.
There's also a lot of background about the old Studio System and about how Hollywood worked in the 40s, especially Warner Brothers.