I'm a on AVS forum when I need to get help or read about Audio & video stuff.
http://www.avsforum.com/
A.G.E is a forum for people over 21 that play video games. They setup tournaments, ladders and game nights. Pretty fun.
http://adultgamingenthusiasts.com/Default.aspx
I use these to computer forums when I need computer help.
http://www.silentpcreview.com/
http://www.forum.pcmech.com/