Red John is Ray Haffner (assuming it's one of the final 5 suspects).
When Red john saved patrick jane in the season 2 finale he used the phrase, "Roll tide", which relates to football. When Ray Haffner asks Cho to come to his office, there's a Heisman trophy behind him, which means Ray Haffner played football in his earlier days. Remember When lisbon asked Ray if he was at the eliston farm in 1980 something (because he was 21 and a new member of visualize), he replied, " we're still friends right?".
He has this creepy vibe and seems to be interested in Lisbon, remember Red john spared Lisbon (thank god :P).
Also, Haffner is a master of surveillance techniques and the physical descriptions fit him perfectly.
I feel when we find out who RJ is in episode 8, and most likely when Patrick gets his revenge, there will still be 5 more episodes in the season covering the "tyger tyger" conspiracy group that consists of people Like Reede smith and many other people in law enforcement. We will also get to see jisbon develop to the point where jane expresses his love to lisbon =).
Sorrry for spoilers but most of this seems true! (all this information was gathered through multiple theories on this site and watching every single episode of the mentalist more than once).
