Top One:

http://www.macdiscussion.com/ the ultmate in discussion, very useable and diverse topics

Links selection:

http://www.osopinion.com/ the top opinion site with broad range of topics, nice sitedesign, cool!!!

http://www.macdebate.com great forum site with an amazing quality feel to it. Serious stuff!

http://www.macgaming.com/forum/ very active forum about games, hints, new secrets, links.etc 

http://macsupport.about.com/compute/macsupport/mpboards.htm support forum, need some registratio