Ruby on Rails Talk is where Rails users come to seek help, announce projects, and discuss all kind of matters surrounding the framework and the community. If you're working on a patch, you can raise issues on the core list. Finally, there's the security announcement list for critical patches.
Twitter & Blogs
Sometimes its just easier to get help or discuss matters in real time. The #rubyonrails channel on irc.freenode.net allows for just that. Try #rails-contrib if you want help or discuss your patch to Rails itself. Need an IRC client?