"The Ethical Slut" by Dossie Easton and Catherine A. Liszt (Greenery Press): All about how to get all the sex, love and friendship you want, without limits, and how to keep it.
"Polyamory: The New Love Without Limits" by Dr. Deborah M. Ananpol (IntinetResource Center): What polyamory is and how it works, by a pioneer in the field.
"Radical Honesty" by Brad Blanton, Ph.D (Sparrowhawk Publications): Just what it sounds like -- how to be REALLY honest and not feel guilty about it, even if gets you in trouble with your parents!
The Polyamory Society
Lots of info and answers to many burning questions, plus lots of links.
Sacred Space Institute
Dr. Deborah Ananpol's Web site. Offers workshops, articles and books on sexuality and alternative lovestyles.
Loving More magazine
Web site of the magazine. Articles of interest on every aspect of the poly lifestyle.
Now under construction, has links to other poly, Pagan, bi/gay/lesbian and related Web sites.