Top Five Spiritual Books for the Serious Reader

I couldn't throw out a "top ten short spiritual books" without asking myself about the other side of the spectrum: spiritual books that were dense, long, and/or not necessarily accessible, but still profoundly worth the effort. Here's what I came up with. I could mention many others that would be worthwhile, but these seemed especially challenging.

• The Denial of Death, by Ernest Becker. This 1974 Pulitzer Prize winning study in psychology and anthropology is a potent spiritual astringent. Becker builds a profoundly compelling case that most of our culture and individual psyche are elaborate mechanisms for denying our mortality. If you want to really get the full effect, read The Denial of Death while simultaneously reading The Death of Ivan Ilych -- then your intellect and emotions will get the full impact of the message and reinforce each other.
• I Am That, by Sri Nisargadatta Maharaj. Nisargadatta (whose honorific name means "spontaneous one") is one of the few spiritual teachers whose profundity can be felt even through writing. This collection of transcriptions of conversations between Nisargadatta and questioners is probably the best way to emerse yourself in Vedantic, non-dual perspective.
• The Marriage of Sense and Soul: Integrating Science and Religion, by Ken Wilber. (Or, really, most anything Ken Wilber has written in the last five or ten years.) Ken Wilber probably has the best intellectual grasp of what's really going on in the world. His "theory of everything" goes a long way to integrating a massive spread of human thinking. There is just nothing that guy hasn't read; for any given idea, he can give you the intellectual geneology of it and name fifty authors who had anything to say about it.
• The Ego and the Dynamic Ground: A Transpersonal Theory of Personal Development, by Ken Washburn. Similar to Wilber, Washburn provides an intellectual model for understanding the nature of spiritual experience. The difference is that Washburn seems to be writing bottom-up, examining real experience in detail and theorizing upward, while Wilber sometimes seems to be coming down from the clouds.
• Tuning Into Grace, by Andre Louf. A monk writing for other monks, Andre Louf provides a roadmap for people who have dedicated their lives to spiritual contemplation. I think you probably have to be many years down the spiritual path before you can begin to appreciate it.