I’m seriously thinking about starting a new forum. That would be a small project though… unless it takes an unexpected direction. Anyway, while searching for forum-related resources, I found this one: The Admin Zone. It’s a forum for forum owners. Besides the many great threads they also have a nice articles section.
I know webmaster forums are usually good places to find useful info about running a community, but The Admin Zone is specialised in the subject, which obviously makes a difference.