At the library, I picked up "45 Master Characters; Mythic Models for Creating Original Characters" by Victoria Lynn Schmidt published by Writer's Digest Books. Having thumbed through and read a bit of it, I think that this book is a must have reference book for all writers. (The link is to Writer's Digest Bookshop.)
This book discusses the major character archetypes in an organized and insightful manner discussing what each archetype fears, cares about, is motivated by and so on. I can see using this book to give one's characters just a little more richness and depth.
In addition to the archetypes, the author also discusses the hero's journey both the masculine and feminine hero's journey. I'd heard of Joseph Campbell and the Hero's journey, but I had never read a discussion about the feminine version of it. The difference between the two journeys is that in the feminine journey, the character changes internally in the beginning and then goes out into the world. Whereas in the masculine journey, the hero goes out into the world and changes because of it. I found the discussion rather interesting and insightful.
I highly recommend at least borrowing a copy from the library and checking it out.