http://www.unexplained-mysteries.com/forum
I tend to gravitate towards the science forums, but it's the philosophy forums that get all the glory. And the UFO/Ghost/I has super powers forums. The best part of the latter is most of them don't understand they're being insulted unless it has bad grammar or workds like "stupid omg lol" in it.
The philosophy/religion forums can be stressful, as there's a little cadre of bigots (GoddessWhispers, _Kratos_, Supra_Sheri, and a couple others) who call themselves "freethinkers" that spend an inordinate amount of time propogating stereotypes, bashing entire groups of people, and trying to eat alive anyone who doesn't agree with them. I finally had to just stop going there. Despite the efforts of the moderators to keep them from doing this, they still do it. The moderators can't keep up with half their bigoted shit and the assholes manage to play the system just enough to keep from being banned. They also will deman evidence from everyone who doesn't agree with them and then refuse to read the evidence presented., saying they don't have time for this nonsense. Or they'll not read it and loudly proclaim that the massive amount of evidence that dares to contradict their (as anyone with a brain can see) obviously erroneous (and most often retarded) theories is nothing more than "religious apologist" works. I don't know about you, but when I think of science journals, I think of religious apologists. Once, _Kratos_ actually pretended I never provided any evidence, despite over and over me presenting it with everything but a giant virtual neon sign. They will also completely refuse to provide their own evidence when asked.
They've kind of ruined my enjoyment of that particular section of the site. I just got sick and tired of saying something neutral like "I like comic books" and them responding with "What do you mean you don't think has caused the deaths of billions of people!?" So now I spend time in forums where people think they can create psi balls, post pictures of a dusty house as proof of ghosts and make snarky comments, engage in debate, and post photoshopped pictures of Ben & Jerry's ice cream. And the science forums too, but nothing ever happens there.
I don't go to the politics forums. I heard the humor and off-topic forums are good. I just realized it's been a couple weeks since I've even been to that site because I've been engaged in other random activity.