My first forum was: www.godfatheruniverse.com - A Godfather fansite, but it's pretty lightly moderated, so there's a bunch of spammers, but it's full of intelligent people, or at least, people who aren't trolls, but I wouldn't recommend signing up to it, unless you want to RP. Plus, some of the better members have left, like me (I wasn't implying that I was one of the better members, but I implied that I had left). Also, I forgot, everyone knows eachother there, so it might be hard to fit in for a new member (though everyone will be friendly to you).
My second (sort of, I went to some forums before it, but it was the only one I stayed at) forum: www.wrestlingforum.com - It's a wrestling fansite, it reminds me of the Escapist, since there are a lot of people there, but there are awesome mods, and most of the members aren't so bad. Also, it has a Rants section, for arguments, where you can get away with flaming, but doing it anywhere else will be an insta-ban. I'd recommend it if you're a wrestling fan.
After that, I found the Escapist, and I currently post here, lurk and post a little at the Fullyramblomatic forums (they have a very trollish community), and doing the same at /b/, though I'm lurking MOAR there.