I'm pretty sure that Red John is Ray Haffner.
First of all, Red John was a member of Visualize. So does Ray.
Also, we know that Red John worked in Elliston Barn. And when Jane asked Haffner if he had worked there he evaded the question.
Red John has decent friends in CBI and FBI.
Haffner had worked in both. And certainly he made some friends. ( Perhaps Bertram? )
Also, Haffner shook hands with Jane on screen. Which can make a strong ground as Heller said "if we watched carefully Red John will be revealed" And he can't name him as good friends of Jane.
On the other hand, he fits all discriptions of Red John. Height, age...
I also believe that Brett Patridge is a strong suspect, too. But as he is fan's favorite. I think Heller won't make you say "I knew it!".
