I lurk on Trader's Laboratory at times.
http://www.traderslaboratory.com/forums/futures-trading-laboratory/
On rare occasions I also visit http://www.bigmiketrading.com/
None of these are very busy, well, not compared to forums like AR-15.com anyway.
Trading is a personal, kind of solitary activity. It's been my experience that talking, and conversing about trading causes losses because you start letting others ideas influence your method. You can look at my posting history for example. I have been here for like 10 years, but I tend to post in spurts, for several months, then I vanish for a long time, sometimes for years at a time. Other places, i am on day in, day out. I will lurk, if I am not posting, particularly in Kung Fu forums.