I enjoyed "A Walk in the Woods" by Bill Bryson
and "Into Thin Air" by Jon Krakaur
one is about hiking on the AT, and the other is about a disasterous Everest expedition.
I also want to read "Left For Dead" by, Beck Weathers, another account of Jon Krakaurs Everest expedition.
Which is available on CD from Amazon
An interesting Book, also written by Bill Bryson, that I have listened to, is "A Short History of Nearly Everything" It is not an outdoor book, but it is quite good. I basically explains everything, from the beginning of time...sort of. :-) And as I think about it, It would be a good book to listen to while hiking, even though it has nothing to do with backpacking