Paula Fredriksen, From Jesus to Christ -- a very readable account of the transformation of Jesus' message in the first few centuries of the common era, not just philosophically and religiously but also politically.
Scott McCloud, Understanding Comics -- an entire aesthetic and media theory in the guide of a comic book about how comic books work. Amazing.
Carlo Ginzburg, The Cheese and the Worms -- using records from the Inquisition, historian Ginzburg reconstructs the diversity of the intellectual enterprise from the side of both commoners and elites during the tumult of Reformation. A constant reminder that intellectual history isn't just the record of great thinkers, it's also the story of how ideas were received and transformed by the population, and how that transformation boomeranged back on the elites.
Erasmus, Enchiridion -- Erasmus is my favorite Reformation writer, and this is his great work on the life of faith. He's just such an amazing prose stylist, even in translation.
David Hume, The Natural History of Religion -- Hume demolishes the idea that religion began with pure revelation and has degraded to the conditions we see today, with wit and irony, in this brief little treatise. Essential to my understanding that every reality we encounter has an evolutionary history.
Elizabeth Moon, The Deed of Paksenarrion -- my favorite book, which I reread every couple of years, a fantasy trilogy about a soldier who becomes an instrument of the gods. You may find it very silly if fantasy isn't your thing, but it's undeniably the work of fiction that has most shaped me.
Shusako Endo, Silence -- For years Martin Scorsese has been trying to make a movie of this novel about Jesuit missionaries in 19th c. Japan. The most powerful portrayal I know of the sacrifice of Jesus.
Laurel Thatcher Ulrich, The Age of Homespun -- an examination of women's lives in colonial America through the objects they made. Reads like a detective story, uncovering something previously anonymous and subterranean.
Marilynne Robinson, Gilead -- A pastor reflects on life and faith and relationships as he nears his own death. Engages with all kinds of great thinkers, but never ceases to be an unfolding revelation of a novel.
Paul Collins, Not Even Wrong -- One of the great non-fiction writers tries to understand his autistic son by digging back into the prehistory of autism.