Dangermom (who can never be anything in my head besides Dangermom, even if she has a real name) recommended this one about Paul a few weeks ago. Since Paul's epistles aren't my favorite part of the New Testament, I decided to read it myself. Sarah Ruden is a classical scholar, not a biblical scholar, who comes at Paul from her own perspective of someone who's completely familiar with Greek and Roman society. Ruden uses Greek and Roman literature extensively throughout the book to illustrate her points. Her book is easy to read, but still thorough and interesting. She focuses on Paul's most difficult or controversial passages and puts them in the context of the time they were written. I've certainly seen this done before on a smaller scale, but not by someone with Ruden's knowledge or ability to write. My only complaint would be that I wanted more, not just pieces here and their about Paul's epistles.
And, like Dangermom points out, this book is rather unpleasant to read in some parts, because Greek and Roman society was unpleasant in some parts.