Recommend a good audio book to buy with iTunes gift voucher?

I'm interested in self-help/psychology/philosophy etc'. I would like to hear from anyone who has found any of the audio books particularly inspiring or useful.
Thanks for suggestions so far
I have Purpose Driven Life in paperback, but never really worked through it - maybe the audio would help me focus. I had Power of Now out from the library but found it impenetrable I'm afraid, but thanks anyway for the suggestion!