Write4Kids calls itself the Children’s Writing Supersite and boy, are they right.  They have a very active message board, articles, tips, advice, and a newsletter.  If you are writing for children or considering starting a book, then this is the place for you. 

MsFrisby.net is filled with reviews, forums, and links for book lovers.  The only unfortunate thing is that the site doesn’t seem to be heavily used or updated recently.  But there are still some treasures to be found.