***This one is interesting. It doesn't really teach you how to write a screenplay. What it does do (and quite well) is identify individual elements of a screenplay and explain what they're supposed to do for the screenplay.
Now, before you shake your head and be, like, "Oh, I don't need that shit," I would recommend you really, really think about how much you know about elements of a screenplay.
Anyway, for those of you who've studied screenwriting in a dedicated manner, much of this book will be redundant. The section called "Screenwriting Tools" is extremely valuable for how it explains and identifies key elements and moments of screenplays without resorting to paradigm. Sadly, it's a little light on the "craft" part of screenwriting, but I found it an engaging read (if a bit dry). Also, keep in mind that The Tools of Screenwriting came out in 1993, before the tidal wave of shit that we have to swim through now.
I also found it intriguing in that most of the book is nothing but breaking down and identifying screenplay elements in popular movies. If you're a film student or an inexperienced screenwriter, these are very much worth your time.
Can't give this one a "must read," but you wouldn't regret it if you picked it up.