Here's my recco's:
Philip Pullman's
His Dark Materials trilogy, which is supposed to be written at a young adult level but it is plenty dark, not dumbed down at all, and has Christian symbolism.
Sagan's
The Demon-Haunted World--Science as a Candle in the Dark is not a work of fiction but I found it quite entertaining.
Oliver Sachs'
The Man Who Mistook His Wife for a Hat, which is also not a novel but a somewhat philosophical and sensitive treatment of a number of very interesting case studies involving brain damaged people.