UPDATE – RootsWeb sites (owned by Ancestry.com) are currently unavailable while they resolve some security issues. If and when the sites are restored, we’ll make the links live, until then, we’ve included the links in parentheses.
RootsWeb (http://boards.rootsweb.com/) and the Message boards at Ancestry.com (http://boards.ancestry.com/) are the same thing. This is a free family history message board.
RootsWeb was purchased by Ancestry.com and Ancestry has kept it as a free offering and they have merged the message boards.
You can search by Locale, Surname, Topic, or Keyword. They boast 25 million posts over 198,000 boards so there’s a lot of content.