Quote from Trvlwanderer:
This may not fulfill the "most popular" status of the OP, but some very good content nonetheless.
It seems to be in the "building" stage, so not alot of traffic as of yet.
Not sure how it is paid for though....no ads.
http://www.trading-lab.com/
I know the owner of that forum. He's not planning on putting up any ads. He wants to keep it as a genuine education-only place where beginners and experienced traders can exchange ideas and learn. I guess he will monetize it some other way at one point.