KB24.com has pretty active forums.
www.forumblueandgold.com is an excellent blog, but I don't believe the have forums.
thelakersnation.com seems to be an active site... we've banned numerous trolls from there already.

(Although undoubtedly there are many good posters there, as well.)
Everyone is of course free to do what they want, but I would encourage you all to comport yourselves in a classy manner on any Lakers site you visit, as the majority of the Lakers fans have done over here. All trolling will do is reinforce a stereotypical image of Celtics fans, and will get you banned. Intelligent conversation, on the other hand, reflects well on everybody.