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Here
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www.mustangmafia.com (Moderator on that site)
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www.autogeekonline.net/forums/ (Mostly lurk and read, occasional posts)
bmxboard.com
miata.net
teamnabr.com
dsmlink.com
supraforums.com
Take those with a grain of salt though. I might go there every day, but I generally spend 3 minutes per site. I don’t really post much. I just look for specifics topics.
team-integra.net
roadrace-autox.com
racepa.com
honda-tech
pgmfi.org
oh and tiava.com 
honda-tech.com (not so much anymore)
lincolnvscadillac.com
bimmerforums.com
member on, but haven’t visited in a few years
racepa.com
I cruise around a few others, but I only post on those three.
www.blazinlow.com
www.smallbizserver.net
www.ephatch.com (hardly ever)
www.s10forums.com (only for info)
barely on anymore but…
DSMTalk.com
Team-DSM.com
dsmlink forums
Slowboyracing.com/forums
ricekiller.com
f-bodyhideout.com occasionally
njfboa.com occasionally
www.vtxoa.com/forums
www.pro-touring.com
www.forums.performanceyears.com/forums
www.jeepsunlimited.com lurker maybe 5 mins a day
http://www.lsxperformanceparts.net/forums/ (rarely)
http://www.ls1tech.com/forums/ (rarely)