http://Team-integra.net Hands down one of the best online community's for any Acura enthusiast.
My home away from home.
-- I banned myself from there since I wasn't getting any work done and wanted to finish my carpc.
Pelican is a BMW/Porsche site but they run the forums to support their business of selling parts. Lot's of lawyers, doctors, pilots and military. lolo, I'm probably the poorest member there but I still drive my P-car :)
www.em2ab.com - for all EM2 chassis (2001-2005) Honda Civics. And I also happen to own this site.
all acura pretty much.
Not vehicle specific but related
Dedicated to diesel engine conversions and focused toward Cummins engines. Involves a large number of highly technical people, but admittedly leans AWAY from computers largely. There is support for those with computerized diesels as well, though.
Site for owners of Ford Thunderbirds, Mercury Cougars, and Lincoln Mark VII/VIII of the MN12/FN10 chassis.
Site for everything Ford 385 series engine (370,429,460). This includes everything from industrial engines to mud boggers to truck pullers to drag racers. Some quite technical people.
Ford Truck Enthusiasts, a site for any Ford pickup, SUV, or truck from the 40s until now.
That's all I have for now.