I believe 3 organizations want to find Red John and in order to do that they need their people close to Patrick Jane and with this theory I rule out some of the suspects.

The Department of Homeland Security wants Red John.  I believe he is part of a much larger matter of National Secuity.  This rules out Robert Kirkland, who is on Red Johns trail.

Visualize also wants to find one of their former familiars, Red John.  This rules out Bret Stiles and Ray Haffner.  I believe Visualize knows who Red John is.  I believe that Visualize through Ray Haffner would know if Gale Bertram or Brett Partridge was Red John.  This could also possibly rule out Reede Smith.  

The Government of CA also wants Red John.  I think this could also rule out Gale Bertram and Ray Haffner as the CBI is using these assclowns to get close to Patrick Jane and find Red John.

Sheriff Mcallister is left.  He had a very small part and I just get a bad feeling about him.  It wouldnt be hard to fill in the blanks and have him as Red John.  Reede Smith could also be Red John, but he could be ruled out as I am sure Bret Stiles knows Red John by description and he probably knows who is working the case.

3 other observations.  When Jane came face to face with the masked Red John, I have to believe the actor playing Red John was a woman but the movements Red John made.  They were feminine.  I cant quite describe it well, but I just get the vibe that it was a chick and not a guy.  Now this doesnt mean that Red John could be a woman, only that a woman actor may have been used.  I also believe that Grace Van Pelt has some connection to this whole plot.  At best she has been converted to a Visualize member, at worst she is some sort of Red John follower.  Thirdly I just dont but that the list of 7 contains the real Red John.  I believe there is some sort of technicality that Heller is using to try to fool the viewers.

Finally I had a really strong feeling that Sheriff Hardy was bad from the second I saw him.  This turned out to be right.  The only other characters I get almost as bad of a feeling about is McAllister and Van Pelt.

Alot of the clues are obviously pointing to Brett Partridge and for this reason I would rule him out. Its the mentalist and like the show name the hunt for red john is the same - one that plays with your mind. I think that Red John is not a group of people as it has already been demonstrated that there is a 'cult / following' attached to what he does i.e loreli, craig so for it to turn out to be a group would be daft. I have no definite suspect in mind but i suspect that it is or should be someone that the whole CBI team know and will be the ultimate betrayal to each and every one of them in some way or another.. RJ will have had it planned all along that Jane would join the CBI so when the truth about who he is comes out the whole team will fall apart... literally. Also, I believe to go full circle it has to be someone who was in the first season, someone we probably didn't notice at the time and may have been in many of the episodes obliviously in the background (if any of you watched fringe, like the observers)