1) Anything by C.S.Lewis, but particularly The Great Divorce or The Perelandra Trilogy, which consists of: Out of the Silent Planet, Perelandra, That Hideous Strength. These books are not only great stories and great writing, but they changed my life in so many ways, I don't know where to begin. They taught me so much about writing, but, more than that, they taught me so much about thinking. Even 30 years after first reading all of the books mentioned above, I still find their stories,images and ideas whispering into and illuminating my journey on a regular basis. Lewis is able to explore ideas, philosophies, and theology, but in such human terms, with so much tender humanity, with so much clarity and grace, that, somehow, in the end, he brings even the most escoteric train of thought home to your particular life experience in a way that will catch your breath & your mind. Besides, the story is always imaginative & riveting... and the writing will teach you, teach you, teach you what it means to see and say.
2) Anything by Dorothy L. Sayers, but especially any of her Lord Peter Wimsey series of mysteries... and, of those, especially: The Nine Taylors Dorothy L. Sayers, like Lewis, was a member of the Inklings, a group of writers that met particularly during the 1930s; the group included J.R.R.Tolkein and was very influenced by Charles Williams & George McDonald. They were predominantly scholars from Oxford & Cambridge, and the quality of their intellectual lives was reflected in the quality of their writing. You will never read a book created by one of the Inklings where you do not enrich your knowledge and understanding in some way or another. You flat-out learn something, usually something fun and amazing, just because these were just inherently smart people! Dorothy L. Sayers writes a mean mystery (and in fact, created the first and still one of the most respected compilations of the mystery and detective genres); never boring, always intriguing, head & shoulders above anything created in the last 5 decades. But, beyond the mysteries themselves is the nuanced, full-bodied creation of character. It is rumored that Sayers actually fell in love with her character, Lord Peter. Whether she did or not, I know that at least three generations of readers did.
3) Anything by James Hilton: The Lost Horizon (won the Hawthorden Prize, which is the English equivalent of America's Pulitzer)...the basis of the movie "Shagri-La. Talk about thinking outside the box! Random Harvest...just a simple, wonderful, moving, evocative story. And Now Goodbye...a story that taught me, to the bone, that every life is a story; that every person, no matter how innocuous & mundane they may appear to the outside world is a universe in themselves! Amazing story.
4) Gabriel Garcia Marquez's One Hundred Years of Solitude, because it will take you outside the box and haunt you with new visions from the moment you read it until the end of your days. I read the whole book in one sitting because I could not, could not stop reading it; it will mesmerize, hypnotize, intoxicate & ultimately capture you forever.
5) Collette's My Mother's House, because it is just one long lyric poem; luscious, delicious, evocative, lovely, inspiring, delightful, and weaves so completely into your memory that you would swear you'd spent some days perched on that garden wall yourself!