In no particular order.
1) Orthodoxy - G. K. Chesterton - This book was the catalyst for my reversion. Too many years of Catholic education had left me unconvinced of the truth of the Faith I was too ignorant to comprehend. Reading the book didn't bring me back, not completely, but it forever disabused be of the notion that the Church offered claims to be taken lightly.
2) The Divine Comedy - Dante Alighieri - How does one praise the greatest poem ever written? Dante offers us a complete education. He is a great moralist, an aesthete, and a sage. No matter how well we think we may know him, he is always there to offer us more.
3) A Mencken Chrestomathy - H. L. Mencken - As David Bentley Hart recently put it: "My affection for H. L. Mencken verges on the idolatrous." Except for Chesterton, no one has influenced my writing more than this joyful cynic.
4) Democracy in America - Alexis de Tocqueville - No one has ever described another country quite so well. While Mencken lambasted democracy for its idiocies, Toqueville praised it for its virtues. But he was also keenly aware of its vices.
5) Brideshead Revisited - Evelyn Waugh. I read non-fiction primarily, but this novel comes close to perfection. Describing the conversion of the head is accomplishment enough. Here, Waugh captures the heart of the matter.
6) Amusing Ourselves to Death - Neil Postman - At long last, an explanation for why television, and now, the Internet, seem to make us so stupid.
7) The Closing of the American Mind - Allan Bloom - To many extents, a very frustrating read, but all the more so rewarding because of it. The book is probably irredeemably political, but it would be better to see here a real professor wrestling with some of the world's greatest thinkers.
8) The Bonfire of the Vanities - Tom Wolfe - The style can be grating at times, but the novel is prophetic. To quote Judge Richard Posner: "American legal justice today seems often to be found at a bizarre intersection of race, money, and violence, an intersection nowhere better depicted than in The Bonfire of the Vanities even though the book was written before the intersection had come into view."
9) The Story of Civilization - Will and Ariel Durant - I'm cheating here, since this is a whole series, but these books provided me the liberal arts education I didn't receive while studying engineering. Yes, they're long, but they'll cost much less than that math class you slept through.
10) The Everlasting Man - G. K. Chesterton - In many ways, Chesterton's best book. Here is the Catholic account of history, the human drama in which we play but a small part. Here is the Faith.