I subscribe to several google groups. It's just like usenet groups/listservs with better organization (and much better searching/archiving). Could possibly useful for a game community rather than a forum because online it's basically organized like a forum (altho without categories, just threads), but the subscribers also have the option to receive posts (or digests) via email.
I used to have my help docs for my game in a CMS/blog, but a couple months ago I set up a wiki (
http://wiki.aethora.com) using MediaWiki and reposted all my documentation there and opened it up to the players. So far a couple of players have made some good contributions. I think it's a great way to go.
(I also have an in-game forum for conversational purposes, but it's kind of basic right now, as I wrote it myself in an attempt to integrate it into the game more tightly.)
