Hmmm...

Well, let's start with Ansel Adams essential trilogy: The Camera, The Negative, and The Print

www.amazon.com/Camera-Ans...pd_bbs_sr_3

www.amazon.com/Negative-A...pd_bbs_sr_4

www.amazon.com/Print-Anse...ef=pd_bbs_5

Even in our digital age, the principles these books explain are fundamental and mandatory.

Straying outside the classics, I'd suggest "Light: Science and Magic: An Introduction to Photographic Lighting" by Fil Hunter.

www.amazon.com/Light-Scie...ef=wl_it_dp

Understanding the art of photogrpahy means understanding the science of light and this is a perfect application of that knowledge.

And, keeping up with the tools of the time, I'd suggest "The Adobe Photoshop CS4 Book for Digital Photographers" by Scott Kelby.

www.amazon.com/Photoshop-.../ref=sr_1_5

Scott covers an encyclopedia of genuinely useful techniques in an in-depth and light-hearted voice that makes a potentially dreary tome into a real page turner. Versions of the book are available tailored to whichever rev of Photoshop you're currently driving.

Finally, I think folks just learning photography are better served to outright avoid collections of other photographers works. While it may inspire effort, the greater threat is that this exposure will dilute your original voice with the influence of seminal work. Better to learn the techniques to capture your own unique vision.

I tend to feel I'll pick up the techniques I need to fulfill my vision. So I'd add to that list, Susan Sontag's book, On Photography, Edward Weston's Daybooks, and Gyorgy Kepes book The Language Of Vision.
Edward's books to give you an insight into the visions and life of a Master, Sontag's book (which I don't totally agree with) to give you insight into the mind of you subject, and Kepes' book, to help you understand how people see. Kepes was instrumental in the Bauhaus movement, eventually moving to America. His book, and to a lesser extent, Lazlo Moholy-Nagy's book Vision in Motion, help us to understand why we feel the way we do when we see something.

One thing I've noticed, is that some of the very best photographer's are unskilled at the tech side, only picking it up when they need to. What they DO understand, without an education on the matter, is what makes a shot stand out, what makes it appeal to us. Shots that can bring a viewer to a stop, and hold them there to admire and view the image, are not easy to create. While I'm not speaking out against excellence in producing an image, I have to acknowledge that some of the images I find most powerful aren't as sharp as they could be, or as well exposed. But the underlying power of the composition overwhelm quality issues.

Once we know what makes an image powerful, it becomes easier to apply that in our efforts to create art. We are blessed with miraculous devices in cameras today, light years beyond what Weston and Adams shot with. This, in my opinion makes our job easier, and lessens the need for massive amounts of technical learning. Learning the basis of the craft in a technical manner from the master Adam's, and at the same time learning how to apply those techniques to overwhelm our viewers, is, I think, the best goal for the really dedicated shooter.