After coming around to critical thinking in the last couple years, my belief in a lot of fringe stuff has greatly decreased.
Bigfoot, Loch Ness monster, Roswell, Area 51, health quackery, the less nutty alien theories, etc. etc.
There are definately 'secret' societies; groups like Bilderberg, Skull and Bones, Bohemian Grove, which are pretty documented at this point. The question is, what are the real purposes of these groups? Reading about them from non-fringe/conspiracy sources is interesting. I recommend the writeups/podcasts done by Skeptoid on these.
It is quite possible the members of some of these groups have fringe/alien/satanism/whatever beliefs themselves, or that there are secret groups within these societies that practice things not known to the general members.