I just updated my "Books Mentioned in My Sermons" list (see the right side of the blog). I've had several books sitting on my desk for some time reminding me to do this, so I'm not even sure when I used two of them.
First, I do recall that I referenced Malcolm Gladwell's book The Tipping Point in my sermon on June 14 about Jesus' parable of the mustard seed. For me, his stories of cultural phenomena gathring steam until a major cultural change occurs seem like a nifty metaphor for the way the way God works in the world--slowly and in seemingly insignificant ways until before you know it something like grace occurs.
Second, some time earlier this year I shared Anne Lamott's story of being ministered to by a member of the ski patrol which can be found in her last spiritual memoir Grace Eventually. Here's a good interview with Lamott about the book at Salon.
Third, at some other time this year, I'm sure when I was preaching on a passage from Mark where Jesus strangely asks people to keep his miracles quiet, I mentioned Brian McLaren's book The Secret Message of Jesus. McLaren expresses theologically and accessibly an explanation for Jesus' strange behavior in a way that surpasses more scholastic and academic treatments of the matter, furthermore, he does so in a way that is prophetic and challenges contemporary Christianity.
I've got plenty more to add to the list. I'll stick them up here some time or another.