No 3rd party books (at least that I know of). I was approached before going on sabbatical to contribute to a book for Cisco Press that contained information about CM, Unity and some other voice/video products but I didn't really have the time to commit to such a project. As far as I know the documentation that that we ship is all there is besides, of course, the forum out here and various white papers and the like on specific topics (i.e. the networking overview, some secruity related stuff etc...).
Jeff Lindborg
Unity Product Architect/Answer Monkey
Cisco Systems
lindborg@cisco.com
http://www.AnswerMonkey.net (new page for Unity support tools and scripts)