I don't think Kristina is Red John. I have many reasons but the most logical one would be she is now too obvious! And when creators make someone obvious, it doesn't usually end up correct!
Though I would not rule out her as an accomplice of Red John! I mean, her indifference when Jane mentioned that she made a mistake, claiming that she said the truth about Red John and things like that.
The twist in guessing who Red John is, is that in those episodes, when they showed that shadow and tea cup (1x23) and the man who poisoned Rebbecca and even when Rebbecca and Rosalind claim that they loved Red John, in the show they never mention that is Red John himself! They could be accomplices for all we know!

I dont really have a theory of who Red John really is, Ive thought it could have been several characters over the years, this is more about how i think the show will end ! I dont think jane ever will catch Red John whoever he may actually be. RJ(Red John) has always been one step ahead of jane from the beggining and i think he always will be that ope step ahead ! Time after time Jane thinks hes going to get him and RJ has ultimatly got some great plan to evade capture and make Jane look like a fool ! The last episodes of season 3 and season 4 are both great examples of RJ being smarter and getting the better of Jane !

As to who RJ really is i have no clue but I deffinatly dont think its Jane OR any of the other CBI Team

I think it's Patrick Jane's father. He's punishing Patrick for leaving the "family business." It has to be someone very close to Patrick and knows him really well, and knows exactly how to push his buttons!

Partrick Janes Brother in law. http://www.youtube.com/watch?v=yYmsod3qlDM

I don't know if we have even seen Red John yet.
He seems to have many tools that he uses and then disposes of them as he sees fit. He could have easily had another tool poison the secretary.
She might have smiled because she knew they were in it together rather than Red John himself. There have been a lot of good points made but I don't think that we will find out who Red john is until the show has run its course.

I don't think Rigsby could kill so mercilessly. He gets too emotional, as in the episode when Red John killed the ffriend of his associate in Mexico.
Rigsby took one look at the bodies and ran out to throw up. He also is too emotional and protective of Van Pelt.

I also am beginning to think that the clues around Minelli are too obvious for him to actually be Red John. He might be, but it seems unlikely to me unless there are more compelling and less coincidental occurences. Incidentally, I really enjoyed "seeing" Red John in physical form last week.
For the first time, he became something other than a topic of conversation. He now is a person, albeit disguised, enveloped and monstrous. Keep the revelations and cluses coming!!

I do not think Rosalind is red john but she must be an accomplice.

Jane is not red john, this is because he could not have poisoined the secretery, the secretery showed no love towards patrick, why would red johns accomplice(police men) try and kill jane if he was red john, jane loves his wife and kids, red john talks to jane via computer, after jane goes to mexico and finds the dead man and the prostitute a man most likely red john calls him and laughs in an evil manner to taught jane. there are so many more that i can't think of right now.

I think red john is a charachter we have only seen once and has been mainly in the background. I really hope it is not minelli because that is what everyone believes and it would be quite boring if they revealed it was him I must admit.

I can't wait to see who it is!