the Dog Park started by The Collared Scholar, (nice general supportive group)
The Truth About Balance Dog Training (pro balance group)
The Canine Paradigm Discussion Group (in combination with a great podcast)
I used to follow a couple of pro-reward only groups and I did get some good advice there but it became too tedious for me to always avoid mentioning corrections, etc, when I joined a discussion. I know that other pro-balance folks were in those groups as well. It is good to get all sides of an idea.