My wife walked through the room the room the other day while I  was watching the show and she commented that maybe Red John is the butchy red haired chick.  I assumed she is referring to Grace.  She bases this on a half assed watching of about 3 episodes of the Mentalist and no other evidence.  I believe this is about as plausible as Red John being BOB from Twin Peaks making a modern day appearance.  My guess: Sheriff McAllister.  He is the only suspect I can't truly eliminate with rational facts.  So little is known about him, the writers could make everything fall cleanly in place.  I also picked Mitt Romney to win the last election and the Redskins to make it to the Super Bowl and win last year.