By request, I'm copying some recommendations here that I posted elsewhere.
I've also read Pagan Polyamory by Raven Kaldera, and enjoyed it. I found it fairly gentle to a hesitant, frightened newbie.
I thought that everyone on the internet had seen (and quoted) this site, but I didn't see it here, so Franklin Veaux's site at http://www.xeromag.com/franklin.html
has a lot of helpful articles. He also has a site called More Than Two.
I really enjoy reading Polyamorous Misanthrope columns. She's got some great common sense answers to polyamorous questions. http://www.polyamorousmisanthrope.com/
There is a lot of information about polyamory in the news here http://polyinthemedia.blogspot.com/
and usually at least one reference to a book worth reading. I think I actually saw this link already in this thread, but I find an enormous amount of reading at Alan's site, so I'll second it.
I *think* I also saw http://www.lovemore.com/
in here somewhere, but I can't quite remember, so I'm putting it in again. I'm not as familiar with this site, but it seems quite kind but helpful.