The Witches' Voice is a Pagan news and networking site, a resource for finding local Pagan groups.
A nice site for basic information is A Rainbow of Spirituality.
Llewellyn Publications is probably the most famous publisher of books about magic and Paganism. One popular one is Paganism: An Introduction to Earth-Centered Religions by Joyce and River Higginbotham (Woodbury, MN: Llewellyn Publications, 2002).
CUUPS is the Covenant of Unitarian Universalist Pagans.