There is some overlap, but join all three. Membership is free.
LinkedIn.com has many great resources—too many to list here. Search for such terms as writers, authors, grammar, publishing, self-publishing, e-books, print on demand, novelist, nonfiction, fiction, crime.
The Midwest Book Review has much useful and well-organized information for writers and self-publishers.
Book designer Joel Friedlander offers information, discussions and valuable advice on a wide range of topics of interest to self-publishers at www.thebookdesigner.com