I'm surprised the SBA (Stephen Batchleor and fans) hasn't been mentioned here:
http://secularbuddhism.org/forum/That would seem the most substantive currently running discussion forum that's closest to DhO in nature (except for the wild-west aspect). It might be seen as s/w dogmatic, s/t fundamentalist, but there are some there who have intelligent things to say and can discuss, e.g. Linda Blanchard, and the guy who does video interviews.
Actually, looking at all the sites mentioned here (SBA and Dhammawheel I knew before), it a surprise that DhO appears to be really the biggest, most active one around. Others may have a lot of categories and/or threads, but look at how many posts for one day (e.g. Feb 10). My quick estimate is that
DhO has more activity, per current unit time, than all the others combined!No wonder DhO might seem an attractive take-over target.