Being Blender free, even if closed source, from start helped a lot in its diffusion, and a wide, stable, active community of users gathered around it from very early.
The community showed its best in the crucial moment of freeing Blender itself and letting it go Open Source under GNU GPL later summer 2002.
The community itself is now subdivided into two, widely overlapping sets:
The Developer Community, Centered around Blender Foundation site http://www.blender.org/. Here is the home of the Functionality and Documentation Boards, the CVS repository of Blender sources and documentation sources and related Forum of Discussion. Coders hacking on Blender itself, Python scripters, Doc writers and anyone working for Blender development in general hangs hereby.
The User Community, centered around the independent site http://www.elysiun.com/. Here Blender artists, Blender gamemakers and any Blender fan gathers to show their productions, get feedback, ask help to get better insight in Blender functionalities.
But, let me repeat it, it's just a single Blender Community.
Another relevant source of informations lies in Blender Knowledge Base, a fully searchable database of questions and aswers located at http://www.vrotvrot.com/support
For immediate online Blender feedback there are three chatboxes permanently opened on irc.freenode.net. You can join these with your favorite IRC client (I'm not going to promote any).
Chatboxes are #blenderchat, #blenderqa and #gameblender. The first of these is accessible even without a IRC client but with a plain Java enabled Web Browser through elYsiun site (http://www.elysiun.com/).