I think Red John is Kristina Frye. She is one of the few people that have the same skills as Patrick and appears to manipulate people with ease. She is also one of the only people that Patrick has had problems reading.

All the evidence points to Red John being a man.. the witness statements, the rape... But if we think about RJ's track record he has always used accomplices and at least one of his accomplices convinced the CBI team that he was RJ himself, therefore I don't think RJ has to be a man. I think RJ has to be someone who can manipulate men to pretend to be RJ. The rape was also not committed by RJ but by the man Lorelei killed in the last episode.

Women are more hated as criminals, it is somehow more shocking and dramatic (which is what the producers are looking for) for RJ to be a woman, especially when all evidence appears to suggest he is a man.

Kristina'a storyline was unbelievable. She was sure that RJ would not hurt her when she spoke of him on TV. This is not a conclusion a normal person would make from looking at the evidence. She then 'vanished' whilst under the guard of Van Pelt (who has also gone a little crazy since spending time with Kristina in my opinion). There was no apparent disturbance she just vanished which incriminates one of them or both of them to me. She is also the only person (to my recollection) who has survived a RJ kidnapping aside from PJ. Her appearance after her abduction was equally strange and unbelieveable. It is also incomprehensible that PJ would have just given up on her after the few minutes of trying to make her talk. She is the only survivor of RJ and she was very close with PJ, you would think he may at least visit her in a later episode.

RJ is a master manipulator with the same skills as PJ. Kristina shares her brilliance with Patrick in manipulation.

The letter RJ left to PJ when he killed his family taunts him about not being 'a real psychic'. Kristina is adamant that she is 'a real psychic.' Obviously real psychics do not exist so Kristina is not to be trusted.

Kristina and PJ shared a connection that explains their fascination with each other on another level - neither like to be outsmarted and both like game-playing.

Kristina appears to be about the same age as RJ may be and we didn't find out about her background.

RJ would not have spared Kristina's life. Also Kristina has sat happily out of view for a few seasons now so that we all forget her.


 

Before I say my theory, I have to say couple of things.

There are many scenes where you can see huge sadness in
Patrick Jane’s eyes when he thinks about his family’s death (example when
Kristina says to him that his daughter didn’t feel pain because she was
asleep). Also, in pilot, when he approaches room in which his wife and daughter
are killed, you can see in his face transformation from his classic smile to
surprise when he sees the note on the door, then to fear when he opens that
door. Why the hell would producers insert those scenes if PJ is the killer of
his own family? Don’t tell me it’s red herring or something it would be just
stupid.

As for ‘He is mar’, it is not written ‘He is Mar’, it is
small m, not capital, so not a name. We definitely know it’s mar not man from
the script. I don’t think Jared Renfrew knew who exactly Red John is. If he
did, why would he bother writing He is.. when he could just write a name. Also,
he didn’t actually said that he knows who he is, he just said ‘I have dynamite
information about Red John’. So, maybe he just knows something that could lead
to him, but not specifically who he is. So, he tried in his dying moments to
write a sentence that could mean something. For example ‘He is married
to...(some person)...’, that person then could lead to RJ. I think he wanted to
write ‘He is marionette’ but i will explain that later.

I think RJ can’t be person that appeared in only one episode
because people who didn’t watch that episode wouldn’t remember him. Producers
are just playing with us with clues like Ardiles==Red sails and Elliston,
Ella’s dinner... just to ask ourselves ‘Is it him? Is it him?’ like Bruno
Heller said. They are also inserting carracters whose names start with Man and
Mar, just to toy with us.

Also, you can forget about CBI Ron and red sweater guy being
RJ because they are not even real actors they are just stunts.

As for Kristina Frye, there is definitely something wrong
with her last appearance. I personally don’t think it is possible to be like a
herb, and in the same time to be a channel to dead souls. So she is probably
faking. Actually my theory is that she is Red John. She is after PJ and Bret
Stiles most powerfull and can have huge influence on people. She likes Patrick,
she is interested in him sexually, like Red John definitely is (sending Lorelei
to examine PJ’s intimate regions). She has a disciple who calles himself Roy
Tagliaferro, and he is the one for whom everybody thinks is RJ, but he is just
marionette (He is mar) of Kristina Frye. He is part of Visualise, and that’s
why Bret Stiles knows about him and has info about missing KF.  

That is my main theory about RJ but I also have little
extension to it. There were many theories that suggested that RJ is someone
from PJ’s past. Remember the little dying girl from flashback scenes with young
PJ. She is called Celia in the script, but I don’t think that matters. I think
that she is Kristina Frye. The girl obviously liked young Patrick and that
likeness (actually ‘form of love’ as Bret Stiles puts it) is only thing
stopping RJ from killing Patrick. Also you have story about that frase ‘Roll
tide’.

As a final thing I have to express my dissapoitment in
quantity of clues producers are giving to us about RJ. I will be happy if the
show is not cancelled before we find out who he is. Also, the facts that
producers put in the show are not perfect. For example, in one episode PJ asks
Rigsby if he put milk in his tea, and in the other PJ says he is lactosse
intollerant. There are others but I think I wrote enough for today :)

Red John said "Roll Tide". At episode 23 of Season 2, when RJ "rescued jane" from fake RJs, RJ said "Roll Tide" to Jane, of which should have only been known to Jane and Frye for which the word "Roll Tide" appeared during their first date.

Also, Frye's disappearance, and than the appearance of RJ in Episode 23 was too much of a coincidence. Frye disappeared in order to resume her identity of RJ to kill the fake RJs.

Furthermore, Frye was someone whom Jane couldn't play mind games with. He could never make her give up her act, much like how he could never make Red John give up her act.

Additionally was the fact she went to TV to talk about RJ with confidence as if she knows nothing was going to happen (because she's red john)

Lastly, the Gender of RJ has not be verified yet. In episode 11 od season 1, the words "HE IS MAN" (of which CBI thought was written by the victim)could well have been written by RJ to mislead people about his gender, making them think that RJ is a he but could instead be a She.

Ever since the introduction of Kristina Frye, i have doubted her of being RJ. 
There was a time when RJs gender wasnt revealed.  The makers always thought it wise to say "Red John" every time instead of "he" or "she"
However i believe only in season 4 Lorelei says "he" and not simply "RJ"
She might have been misled...

RJ is definitely a manipulator, I dont think only money would actually make anyone do things you want.  There has to be some persuasive powers involved to make someone do it and actually believe that what they are doing is absolutely right.
The only people i can think of who have these persuasive powers are Kristina Frye and Patric Jane.  If PJ is really RJ, then i think it is pretty lame, so KF is my next best suspect.

KF and Patric Jane are more or less adversaries trying to prove a point of whos  best, It gives KF enough motive to keep haunting Jane as RJ and keep him alive to enjoy seeing him being defeated every time

I think KF staged her own abduction by RJ so as to remove any doubts of her being RJ herself.  Its the most perfect alibi.
If she were indeed abducted, why did she take her passport and other things with her? and then why did RJ keep her alive...Keeping Jane alive is one thing as RJ obviously enjoys it but whats the point of keeping KF alive, it just doesnt add up

When KF was recovered, the easiest way to escape any kind of interrogation about RJ was to plead insanity which is exactly what she did.
and then she suddenly vanished.  The very fact that jane has never tried to go to her again and try to stabilise her emotionally to get information about RJ is suspicious
If Jane is trying hard and banking on the smallest of small leads to get closer to RJ, why hasnt he tried to approach KF again to get any info possible on RJ.  If she has really gone crazy, why doesnt he try to hypnotise her and then gather information

The makers obviously are trying to take KF away from the spotlight so as to bring her again suddenly as a big shock and surprise

The Mentalist has always been known for strange twists and turns.  Wht bigger surprise and twist than the fact that Red John is actually a woman !!!

Kristina Frye is a mentalist as Patrick Jane . She is so damn clever . she some times solves things before Patrick Jane does . And when the scene happened that Red John kidnapped her . she took her passport with her and her stuff . Red john didn't kill her because she is Red John . when she decided to come back and show her self , she claims that she was hypnotized to believe that she is dead so that Jane doesn't suspect her . And If you rewatched S2 E22 and E23 and the day that she return you will find out her actions . She shook hands with Patrick Jane and they we're not friends . remember when Jane went to the bathroom :) . He was gonna tell her some thing that he can't stay with her , but he got a call for the office .

SHE is RED JOHN. They shook hands.

http://www.youtube.com/watch?v=hSiB1q67fY8

This one comes in form of a question. Why was Frye so confident about speaking about RJ in the media when she knew something bad might happen to her?? But behold, RJ spares her life but kills the lady that interviews her. Makes no sense! Next time we see Frye, she seems to have been turned into a ghost or something, mehh! I don't buy that. SHE IS Red John or a reliable RJ associate, else she'd be dead as soon as she went on air with RJ's name asking 'him' to 'get help'!