Mavericks mavtalk.com Kings bleacher mob or something like that...You should be able to search for it.
Spurs: http://pub1.ezboard.com/fspursreportspursfanfeedback Warriors: http://www.bomis.com/rings/nba_warriors/ NBA Fan Forum: http://www1.tamado.com/commu/?Q_cid=142 RealGM has some forum stuff as well.
a list of NBA team message boards for every team in the league... http://jazzhoops.net/special2.htm yeah, its a link off the dreaded Jazz fan site, yuck!