Oh boy I am giddy about replying to this thread...hahaha I am such a nerd. While I admire narayan's tastes, I would add 'The Prophet' by Kahlil Gibran if you are looking for spiritual literature.

'The Poisonwood Bible' by Barbara Kingsolver
fiction-follows a baptist missionary family into the Congo and chronicles the challenges to thier faith, identity, and understanding of mankind and the natural world. Very 'Heart of Darkness'-esque, if you have ever read any Conrad, another one of my favorites.

'The Sea Around Us' by Rachel Carson
non-fiction- an environmental writer, Carson is most well known for her more politically charged 'Silent Spring,' and as an environmentalist I appreciate her contributions to the American conscienceness, but as a writer I prefer her subtler works. Yes, this is a scientific look at the ocean, but to read it is like a book of poetry; your entire relationship with the sea will change.

'Grendel' by John Gardner
fiction- a retelling of the epic poem 'Beowulf' through the perspective of Grendel, the monster of the original. Beautiful, sad, enlightening. The classic man vs. beast argument here, examines the real definition of "humanity," its purpose, its rituals, its consequences. It's a quick read, but you will find yourself going back to it again and again.

Well there are so many more, but I am going to cut myself off before I go any further. I think half the fun of discovering new books is the story behind how they entered your life, so I keep my reccomendations brief...have fun!