This isn't a theory ... I would just like to say that i'm having a couple of problems buying the last episode ...
First ... The list ...
Well ... How could RJ get precisely the same list as Jane???
And how come, in jane's list, there's no one from his carnies days or from his psychic days??
He said that the list had the only 7 people that could have been in every crime places ... Really ???
Nobody from his preview life (before CBI) could have been in every crime scene????
But ... continuing ... In the Red Barn episode, we heard, and so did jane, from a priest that a "kid" was painting the smiling face .... Well that was in 1988 ... So the person would have to be 30 (TOPS) in those days ... Well ... Jane knows this ... but RJ didn't know this ... So i can understand why stiles is in RJ's list ... What i can't understand is why is he in Jane's list ... He is too old !!!!!
And ... Last but not least ... How could ANYONE know that Lily Barlow was a happy memory for jane if he didn't tell anyone?????
I guess he could have told in the carnies days or in the asylum but ... Wouldn't he remember telling??
I mean, really people, think a little bit?? Does anyone know who is and who is not in your memories??
Nobody can know that if we don't tell them ... Not our parents, our siblings or our best friends ...
Because, we all have had several happy moments in the past ... And sometimes we don't even know why we remember one more than another ... So how could someone else do it ???

The matter of the fact is that the writers have dropped massive hints and clues for most of the 7 suspects. At least the ones we've seen a lot of, and I'm sure Heller will be dropping hints for Reede Smith and Thomas Mcallister in Series 6.

Here are some of the big hints we've seen already:

Bret Stiles:
-Gave Jane the location for Kristina Fry
-Described the release of stress as a "red cloud" to Van Pelt.

Bob Kirkland:
-Overall suspicious manner. Seen in the Limo for example.
-Killed Lennon, plus the "Do you recognise me?"
-Drank a Bloody Mary, the same drink Jane has three of on the anniversary of his family's murder.
-Similar voice.

Brett Partridge:
-Too much enthusiasm when dealing with RJ cases.
-The scene when PJ surprises him is mirrored with the Red John scene in "Red Sky at Night"
-Similar voice
-"Partridge" - it's connections to Blake

Gale Bertram:
-Reciting Blake's poetry.
-His mystery vacation while leaving the team without a license to work.

Ray Haffner:
-Right after it's revealed that RJ was a member of Visualize....Tad dah! Haffner is revealed to be a member of Visualize.

Even minor characters like Ellis Mars have had big hints dropped that they may be Red John, so it's really hard to know what's relevant when you have no evidence and it's purely theories.

Here are some questions that have been left unanswered:
How did Red John know about "Roll Tide" in Red Sky at Night? Was he at the date?

Why didn't Red John kill Bret Stiles if he knows information about Red John, and is willing to tell Jane some of it?

What did Bosco whisper in Jane's ear the moment before he died?

The answer to the last one has still been hidden away from us and may come into play at sometime. I'm just hoping the writers haven't thought we've forgotten about it.

Red John can't be Bob Kirkland...I mean he killed a man in a hospital!
Red John doesn't make the "minor" kills.He kills when he wants to get
Jane's attention and always leaves a smiley face at the crime scene.The
exception would be in the season 2's finale when he shots 3 teenagers
and cuts the girl's neck.But he did that just because there wasn't
enough time to kill them in his notorious style. Sorry for my
English,it's not my native language.

A lot of great theories and speculation on here but my main suspect is Sheriff Tom McAllister.

A lot of great points are made as to why it is plausible to be him with Theory #3066 on this site. I won't rehash those valid points but here is a new one to consider:

In episode 2 of Season 1 where McAllister is featured he appears to be looking to prey on Grace Van Pelt before Rigsby intervenes. He acts shocked that they would think he would be a killer. In the words of a famous English playwright "Me thinks doth protest too much!"

The seed has already been planted with McAllister.

Did anyone realize, that the character and charisma from Ray Haffner did changed radically  in the 2 Episodes when he appears? In Season 2 Episode 2 PJ was in Haffners Team, because lisbon was suspended.. but he wasn´t able to manage and Control PJ, he was too smart for him. And they shoke hands. Interesting: In ths Episode Haffner, Betram and PJ sat on the same office. PJ and 2 RJ suspects in one room. Was that a coincidence? I dont think so. In Season 5 Episode 13 (or was it 15?..nut sure yet ) the charisma of Haffener had changed radically, as is said above. He offered Lisbon a new Job and a new life, like Lorelei did with PJ. RJ is very interested in Lisbon, in the Last Episode from Season 4 he wants Lisbons head.

Brett Patridge is a sociopath, but not charismatic enough to manipulate so many member from FBI and CBI... is Patridge really able to manipulate people on this way, that others people would die for HIM, like Timothy Carter and o Laoughlin? i think not.

Perhaps Patridge is really Red John, butI am sure that Bruno HEller is reading this site and our theories. And he can see that so many prople suspects Brett Patridge. Because this, i am pretty sure that he would change the script.

Well they say red john is in the list but do we know there is just one person. Or let me say it in another way, even if there is A red john, there are mor people in that list that serves to Red John. And there is nothing  against that. Bob Kirkland is working for Red John that's for sure. From him Red John learned  what info Patrick has and find out there are only 7 people left. So Bob Kirkland is just  a servant of Red John otherwise there is no mystery there. Also about Brett Partridge, well there are  lots of theories that says it is him but I do believe he is either a missdirection (which is the main concept of this program) or another servant of Red John. I honestly believe Red John is Sheriff McAllister. Why? Well it is impossible to find a clue from a guest appearance from season 1 but the magic word is STAR POWER.
Even fake Red John at the end of season played by Bradley Whitford. Xander Berkeley is the biggest STAR in the list and the most mysterious one.  

Unless PJ is one step ahead and faking for everyone (even Lisbon), that seven names are really his list and RJ is really too ahead. But I think it was really a work of genious of Red John, cause how could he know that there was 7 names, not 6 or 8?
Remember that the video with Lorerei was recorded at s05e16 or before and Jane's attic was invaded by Kirkland (only on s05e19), so it was not from there that RJ made his list. Due to this, Kirkland is for sure not red john.
Heller will have a hell of a work if he wants PJ to win this game.
In fact, the only way I see is if PJ and Lisbon simply arrest or kill all seven suspects as fast as they can.