The Road by Cormac McCarthy. Not a book that brings a smile to your face, and while I was reading I felt annoyed at wasting my time on such a depressing novel. However - the discussion from that book remains one of my favorite discussions, and it totally changed my perspective on the novel. The discussion brought a new dimension to the novel and completely changed the experience for me. I try to do this with my children - especially when they have a hard time getting into a book I know has value (Johnny Tremain comes to mind).
Recently, I've contemplated the benefit of discussion groups and wondered about starting a discussion group for my daughters. (My oldest daughter asked me specifically about starting a group, and I'm investigating whether this is a feasible option right now.) This got me thinking about starting (another) book group for me - one with fellow homeschoolers. I find homeschoolers to be an interesting and eclectic group, which makes for a great discussion group. I'm just not sure I know enough homeschoolers in a small enough geographic area to make it happen!
Oh well, something to think about!