Nr. 1 Ironwar by Matt Fitzgerald
Yes, I know this is not a running book per se, but I think runners can get a lot out of it. Matt Fitzgerald is an amazing writer. He is able to combine the story of 2 of the greatest ironman triathletes Dave Scott and Mark Allen, with science on running form, running efficiency, mind-body connections as pertaining to running. I absolutely loved the conclusion of his book. Yes, the mind is important, but the ability to push through and suffer is somewhat determined by your genes. This is not to say that life experiences (e.g., childhood struggles) and training experiences (how much you practice suffering) are not important; they are, but not as much as what you are born with. It's a bit like the nature-nurture diathesis - we are born with a range of "suffering ability" and we can get to the top of that range by practicing, but we can't get further than that.
Nr.2 The Runner's Body, How the latest exercise science can help you run stronger, longer, and faster, but Tucker, PhD & Dugas, PhD, with Matt Fitzgerald.
This is a 2009 book, but I reread it during this past year. I love reading and understanding the science behind running. These guys present great info and clarify some of the misconceptions about running (e.g., cramps are caused by dehydration or lack of salt, we need a lot of fluids when running, etc). The book is much more than that, however, and I think it is an important one for all serious runners.
Nr. 3 Tapering and peaking for optimal performance, by Inigo Mujika, PhD
This is a great book about tapering, and provides research on the psychological and physiological effects of tapering.