For the beginner:
After you've written a few screenplays:
Advanced (written 5 or 6 screenplays):
Once you're ready for the market (business side of screenwriting):
As for other popular books, I'm not the biggest fan of Robert McKee and therefore don't recommend "Story". It's very dense and too scientific. You can drive yourself nuts trying to write a screenplay under his rules. Although I don't discourage people from buying "Screenplay" from Syd Field, I think it's a bit outdated. A lot of people love "Making A Good Script Great" by Linda Seger but I just didn't connect with her approach for some reason. There are a lot of middle-of-the-road books that I'd rather not take the time to mention, however, if there's a book you really love and think people should know about, please leave it in the comments section.