Freethought Forum - This and my Facebook feed are my primary sources of news. There are some really knowledgeable people here, including several lawyers and scientists.
The Lifestream - Final Fantasy board focused around the Compilation of Final Fantasy VII. This board has some of the best discussion of Final Fantasy VII and the Compilation on the entire intarwebs. I admin here.
Fool's Gold - My own board. Frankly it's in a terrible state right now and I'm not really sure what to do to clean it up/revive it.
There have been others as well but most of them died or I got bored of posting there. And I guess if last.fm groups count I'm active in some of those as well.