Communication Arts Magazine
This is the book that started it all for me. No one should be allowed to call themselves a graphic designer if they don't have a copy of this book.
Running a close second to Milton, if not in front at times, is Seymour. I had the pleasure of showing him and his wife, Paula Scher, (a design god in her own right) around Albuquerque back in 1989 as a part of speakers conference our advertising club had.