/r/mistyfront ... subreddit where a bot posts top posts of other subreddits. Very varied, good content. /r/tulpas ... People who try to make a sentient being inside their mind using practice and self hypnosis. I don't really follow it, but it's a weird and cool idea not many people know about, and it seems to work for some people.
Came here to suggest http://reddit.com/r/Tulpas. I accidentally joined the community a month or so ago as the result of research into how gender identity works. Now, I have a female voice in my head along with my own & we're studying the potential therapeutic/developmental reasons one might choose to create a Tulpa.