I wanted to provide a list of books, that we use and recommend for both staff and customers for reference and becoming more familiar with IPv6 in general. If you have any reviews of these books specifically or want to recommend other titles, please feel free to share!
O'Reilly's IPv6 Essentials By Silvia Hagen & IPv6 Network Administration By David Malone, Niall Murphy
Both of these books cover the very basics of IPv6, as well as branching out into much more detailed information regarding the protocol. I consider IPv6 Essentials mandatory reading, especially for a technical support role.
Apress' Running IPv6 by Iljitsch van Beijnum
Excellent guide for getting IPv6 up and running on a variety of platforms.
Microsoft's Understanding IPv6 by Joseph Davies
This book covers both a detailed introduction to IPv6, as well as getting it up and running as a client or server. It has information spanning XP/2003/Vista/2008 platforms, and the pros and cons of each.
Morgan Kaufman's Theory, Protocol, and Practice by Pete Loshin
A good resource that covers what is wrong with IPv4, how IPv6 can help, but also some of the problems facing IPv6. It has a bunch of configuration examples for operating systems as well as Cisco appliances. There is a really decent section on real-world IPv6 security practices, as well as configuring Internet services that are a must like DNS, Email, etc.
Planning for IPv6 by Silvia Hagen
Another well written and composed book by Silvia that addresses testing, implementation and deployment of IPv6 into your lab and production networks.