I just read a very good article about online communities. This article by Nancy Strauss – Should You Launch a Brand Community? contains excellent pointers.

For instance, What Is an Online Community?

Often, the designated community sections of corporate and e-commerce Web sites do not actually function as online communities. Instead, they are pages where the company posts content for its customers, or they are message boards where visitors can publish comments on specific topics.

Online communities are about the formation of relationships among Web site users. To achieve that kind of interaction, certain factors have to be present:

1. The members have to be visible to each other.
2. The members have to have a way interact with each other directly on the Web site and a reason to do so.
3. Members need to visit the Web site regularly over a period of time in order to get to know each other.

Read more about this at:

http://www.marketingprofs.com/9/should-you-launch-brand-community-strauss.asp?sp=1#storyContinued

You could see examples of this by accessing NING on the Net. Another very good example is Speakersite. This is a community that I belong to.