For 4chan, I generally go on /x/ (pretty much only due to interesting creepypasta, most of the people there are crackpots), /vp/ (Pokemon), /wg/ (easily the best place to get beautiful, engaging wallpapers).
Never heard of it.
It's basically a video-game humor/review site, definitely really engaging, and a lot of video game figures write articles there (Jim Sterling, Felicia Day, etc.)
Same goes here.
A incredibly relaxed debating site. I used to frequent there quite often, but I've started to wean off of it. The admin tries to be as lenient as possible as to what's o.k. there or not. Often times, you can dick around if you don't go to the polar, polar extreme.
Duh! Any good youtubers?
Angryjoe, Totalbiscuit, Jessecox, Seannaers, Dodger, Marikiplier; that's basically it.
Now why would you use RT and imdb?
I'm a movie junkie, haha. Rottentomatoes usually gives me first impressions. I mostly use imdb for general information (casting, expected release dates, etc.)
Never heard of it.
Another videogame site.