Mailing Lists:

 

 
User Groups:
Joomla User Group Directory
http://community.joomla.org/user-groups.html
Joomla user groups around the world.
 

 

 
Discussion Boards:
Joomla Discussion Forums
http://forum.joomla.org
Official Joomla discussion forums.
 

 

 
Chat Rooms:
irc.freenode.net
#joomla (unofficial)