Here's a pile of forums I've found on the net over the past months and years. I'll post them all here as they might be useful or at least semi-interesting to some users here.
Just for fun (ya, fun stuff for me is likely different than most peoples definitions ) I threw them all into a spreadsheet and ranked them all by "highest number of posts per thread" and this is the ranking I came up with.
I was trying to come up with a rough metric to find the "chattiest" forums... even among those that were somewhat smaller in user base size than the BIG BOYS like trade2win, elitetrader etc.
Forum - threads - posts per thread
forexfactory.com 20834 51.45
hotstockmarket.com 46662 38.92
sharetrader.co.nz 5649 38.57
aussiestockforums.com 11248 34.56
forex-tsd.com 7231 34.01
sharesforum.co.uk 3263 26.35
allstocks.com 52753 21.6
stockmarketcats.com 2624 16.8
elitetrader.com 122463 16.14
oanda.com 27648 14.43
traderji.com 17332 14.16
traderslaboratory.com 3982 14.15
trade2win.com 39600 13.54
createphpbb.com/phpbb/?mforum=fxreview 1818 12.98
forex4noobs.com 1188 12.95
nuclearphynance.com 9420 12.57
kreslik.com 1430 11.01
forum.fxopen.com (English FX section) 3169 10.9
moneytec.com 48051 9.28
fxstreet.com 1706 9.09
traders-talk.com 48200 9.01
smartquant.com 1830 8.51
fxfisherman.com 3009 8.17
forexforums.dailyfx.com 14442 7.68
tradestation.com 47331 6.85
tradingblox.com 2196 6.81
sierrachart.com 11869 6.04
thetechnicaltrader.net 1068 5.69
talkgold.com (forex and investment sections) 14713 5.19
forum.tssupport.com 3695 5.05
woodiescciclub.com 2285 4.99
babypips.com 18539 4.82
money-talk.org 9463 4.73
forums.marketocracy.com 16619 4.2
goldage.net (forex and investment sections) 5029 4.1
forexforums.org 128565 4.04
forexpeacearmy.com 3131 4
piptrader.com 1024 3.86
stockhideout.com 1862 3.66
forums.fxinstructor.com 1196 3.39
forexnews.com 1689 3.28
mataf.net 8394 3.02
slashinvestments.com 330405 2.61
forum.alpari.co.uk 2729 2.58
forexforum.net 6109 2.08
forexboards.com 2109 2.03
onlinetradersforum.com 106402 1.97
forexforums.com 7409 1.47
einvestorsforum.com 2418 1.23
forexscamcheck.com 17962 1.07
websitetoolbox.com 2359 1.04
informedtrades.com 363711 1.03
fxcomparison.com 27376 1.01
moneymakergroup.com (investments section) 72736 0.47
traderscommunity.com 102161 0.17
mypivots.com 40782 0.09
3 more moderately large forums where it's too big a job to count all the posts to calculate posts per thread:
Forum - threads
wilmott.com 65307
investorvillage.com 14736
forum.mql4.com 6905
There's a huge variety of forums in there covering all sorts of trading and investments. Enjoy