First of all, i love The Mentalist but the idea of a serial killer with a network is completely ludacris.
Organized crime bosses and serial killers have two very different types of personality ...
I think that the theory of jane being red john is funny but impossible for many reasons described before, mainly because most of the people in red john's network that met jane didn't face him as if he was red john, specially rosalin harker, timothy carter and lorelai martins.
I believe that red john could be one of three persons ... Brett styles (even though i think he is too old for the character), brett partridge (in this case i think he might be too young) ... And kirkland ...
Kirkland is old enough, has power, means, money, connections ... He killed a guy who could identify red john on 5x18 ... He seems very aware of everything and seems to know jane pretty well but jane doesn't know him at all ... Besides ... the theory that he couldn't be red john because of lorelai being in prison at the time he and jane shook hands, doesn't convince me, i believe that he had met and shook hands with jane before that instance ...
Other theory is that Kirkland is another of red john's friends ... And in that case Ray haffner seems a good suspect ... He might have been in the  visualize farm when the red john face was painted ...
He is a member of visualize, and that gives him some kind of power and connections ... besides ... styles might be another of his friends ...