One hesitates to recommend prose non-fiction: there is too much of it around. Even if one manages to peruse a sizeable chunk of it, as I do, one has difficulty choosing between books that are interesting but add nothing to what is already general knowledge, and books that make you think anew. The latter are in short supply these days, though I believe my list - with the inevitable omissions due to sheer lack of reading time - contains books that do make the reader pause for reflection.
People hate him or love him. But for me, Terry Eagleton is not just a particularly refined intellectual but one of the most stylish of living writers of the English language. In Reason, Faith, and Revolution: Reflections on the God Debate, he brilliantly relates to the current debates on God and faith, as an atheist who takes religions seriously and treats them fairly. His focus is on Christianity, but his larger arguments remain valid in other contexts too. From a believing Muslim perspective, a more personal and less intellectual engagement is provided by Tariq Ramadan in his What I Believe. Both are nuanced incursions into matters that often make many intellectuals (not to mention 'believers') shoot wildly from the hip.