Hatteras Yacht
http://www.hatterasyachts.com/news.cfm
Angler
http://www.angler-boats.com/angler_boat_index.htm
Contender
http://www.contender.com/
Bayliner
http://p076.ezboard.com/bbocweb
Sea Ray
http://www.searayowners.com/
Sea Doo
http://www.network54.com/Forum/143168/
Yamaha
http://yamahajetboaters.com/forum/index.php
Iboats (sectioned individual group Manufacturer segregated)
http://www.Iboats.com
Parker Boat Owner Forum
http://www.classicparker.com/
and of course Triumph Owner forum
All owner forums that are as you mention, brand specific.
There are a plethora on the WWW, the above are just to name a few