I Guess It's Up To Me To Kick Things Off Here...
So... Here are twenty books for ya'll to consider (I intentionally chose too many and repeated some authors hoping something here would provoke conversation),
Till We Have Faces
Lewis' exploration of love, holiness and longing was though by him to be the best of his stories and it's easy to see why - it's richer and more complex than almost any novel I've ever read.
The Lord of the Rings
Now we come to the only book I know of that's competes in the "rich and complex" category. We all know it's a good story but have you taken the time to explore the themes of Mercy vs. Justice, Evil's Effect on the World and the Role of Providence?
Watership Down
The best adventure/dystopian/pilgrim's-progress/folk-story/parable starring rabbits ever written!
The Man Who Was Thursday
Plato's concept of philosopher kings was interesting, G. K. Chesterton's philosopher policeman are just plain cool.
Brendan
Buechner's bawdy romp through the life of St. Brendan the Navigator leaves us scratching our heads at why the roman catholic church doesn't call us saints and, more importantly, why God does.
The Storm
The most moving story of forgiveness I've come across in a long, long time.
Fahrenheit 451
What would the future be like without books? Bradbury offers gives one possible answer in this startling dystopian masterpiece.
On the Road with the Archangel
In the tradition of the brothers Grimm and other weavers of fairy tales Buechner offers reflections on things like love, prayer and relationships in a tale that is pure joy, from start to finish.
Some Others To Consider (Without Capsal Reveiws):
Cry, the Beloved Country
Godric
The Last Battle
The Great Divorce
Something Wicked This Way Comes
Short Stories, Flannery O'Connor
To Kill A Mocking Bird
Perelandra
A Wrinkle in Time
Pilgrim at Tinker Creek
Sophie's World