See also the WikiNode.
If you're mainly interested in reading about online communities, rather than discussing them, here are a few interesting places to read:
If you want to discuss something other than online communities that is covered on MeatballWiki:
If you want to discuss something other than online communities, there are a few places you can look for something suitable:
If you want to start your own wiki or wiki-weblog, here are some quick pointers: