Heh. The New Love Without Limits is a book I recommend people avoid because it has far too much New Age fluff crust to truly be useful, in my opinion.
Jenny Block's book, Open: Love, Sex and Life in an Open Marriage, is an interesting place to start.
I also recommend Opening Up, by Tristan Taormino. Of the books I've read on polyamory (and I've not read all available, as yet) this is the one I think provides better coverage and discussion of all aspects of non-monogamy, which helps provide a better understanding of how polyamory fits in with other forms of non-monogamy.
Thomas Moore's The Soul of Sex is a book I found quite interesting. It doesn't deal specifically with polyamory, and has quite a lot to do with relationships and marriage.
When speaking of various forms of non-monogamy...it ain't poly if you're just fucking around.
While polyamory, open relationships, and swinging are all distinctly different approaches to non-monogamy, they are not mutually exlusive. Folks can, and some do, engage in more than one of them at a time--and it's all good.