Suggestions?

I also wanted to mention here briefly that I've been listening to a lot of audiobooks lately when I go running (which is becoming a serious time commitment, by the way!) and I am just running out of Sherlock Holmes. I was thinking about getting Adventures of Huckleberry Finn as my next one, but I am open to suggestions. Any ideas for what I should listen to?  It should be interesting enough to keep me going during that grueling 4th mile, but it doesn't necessarily have to be crash-bang action.  Let me know! :)