It became clear it was an organization several seasons ago,there were signs everywhere that Red john needed followers to have control . Somehow killing is just a hobby, his way to keep balance.
As for the suspects, All of them lack the charisma to be Red john, Red John is proud of himself, he consider himself having a higher path to change the course of things, so his ego won't allow him to hide himself into a lower caracter, and plus he must have the ressources ( Making companies, spying, buying proporties, flying to mexico in a jet.. )  to maintain the ropes in his hands. 
Now you can ask yourself about the charachter that would fit immediatly into this without even thinking of the clues : Walter Mashburn. Even that he had appeared only 2 episodes he is being remembred well !
Walter Mashburn is brilliantly smart, you can see it in the way he talks, the way he choose words, and the way he keeps his smile while maintaining quite a dominant prescence. He have the right Charisma : the one that someone enjoying a cup of tea while listening to Bach, and call PJ And TL Patrick, Teresa.
The scene of Teresa and Mashburn getting laid, his phrases such as " Try and catch me. i hate to lose and i am quite canning. ) He even diagnostiged himself and found a pleasure seeing Patrick trying to analyze him, it is like he was shouting it loud ' I AM RED JOHN"  as they say : the better place to hide something is on the sight of everyone.
Also, Patrick even enjoyed his company more than anyone in the show,  And now his way of changing a subject to an other one as a tool to play the mind of others, rewatch again and see how subtil Mashburn is and that makes him look quite alike him and Patrick, somekind of a symetry, he even got Teresa played well : he got her into his bed. ( No need to talk about a rivalry here between RJ and Patrick, as for getting Teresa, even if it is quite obvious. )

Now let us look at the official clues, they all matches  : 
     - he looks a bit cacausian. 
     - his age
     - his height. 
     - short straight hair. 
     - the voice ( in the video, when he was coming in the boat and he shouted : Patrick )
Here is a video that summarize some highlights in the episode where walter mashburn appeared. : http://www.youtube.com/watch?v=JU8MN9WJghE 

The choice of Mashburn will guarantee that the Mentalist would stay one of the best series for a long time, and also if we got to see him more often into this season. 

And if the writes chose to play it in a commercial way, i would be disapointed same as everyone who doesnt watch Television much and got into being somehow of an addict to the show. If he is in the list : Haffner would be Red John as bad as it sound. 


As for the theories of Ellis mars, CBI Ron or other charachters that are barely remarquable, please enlarge your horizons a bit, we are talking about a criminal mastermind, so Red John must be some one that have some weight as his real charachter.
And i do believe that RJ first was Partridge, but the writers changed it because people were waiting for something more brilliant. Also, the mass of the clues that you are watching are only for the show.

And a last point to make : 

I THANK YOU, YOU ARE THE TRUE WRITERS OF THIS LAST SEASON. THIS IS THE PURPOSE OF THIS WEBSITE : TO SEE EXCPECTATIONS AND TO GO BEYOND THEM.

Now please, feel free to point any lack of logic in my theory, i need anti theories and we should work and develloped the theories here.