I don't know if all of you remember this bizarre character that was introduced in edpisode 3x9 "Red Moon". It's a bit strange because when a character is introduced in has something to do in the episode, right? I mean, is not just put in there without an epilogue. So I think that RJ is Ellis Mar: http://4.bp.blogspot.com/_jBuO6o0VUr8/TRbZ_hcNBRI/AAAAAAAABOU/1Y1n8GsMKKw/s320/billingsleythementali...

Supporting my theory I say:

1. Is older than Jane so it is appropriate (he must be older)
2. Is a mentalist like Jane, a good one.
3. In season one... the writings on the bathroom wall made by the prostitute "He is man\r" can suggest that the escaped prisoner(lol I don't remember the name) said to the prostitute to write the name (because you can see that was the prostitute that wrote the name) but he was dying and spelled is wrong.
4. It is an insignificant character, no one knows and also laughs about him, thinking he could be RJ. That fits more than ever in my opinion, because in the series style. You don't know what's happening till the very end. Just think of it:

-You realize Brett Partridge is RJ ---> meh guessed
-Or Brett Stiles ---> lots of theories
-Gale Bertram ---> as above
And I can go on and on with almost every character portrayed in the show, no one would give a damn that Ellis Mar is RJ. Sorry for long post.

You guys Red John is Kirkland! It's so obvious that's brilliant! Or Brett Stiles

I'm not sure about many Red John theories but there are many I find quite plausible. However, in Season 4 there is a reference to another William Blake poem. It was in the episode where Highttower escapes. The Director, Gale Bertram, and Laroche both laugh at the poem that Gale recites. I think we all also remember the poem by Red John, Tiger Tiger, also by William Blake. 

Robert Kirkland is the one can't u see it guys 

Van Pelts Father: O'Laughlin says something to her about her father when they meet and seems impressed/intrigued. Also her father is mentioned by Jane in the pilot episode. Don't know if they shook hands though.
Another clue could be the words scribbled on the floor... HE IS MAN =  Heisman Memorial Trophy Award (The Heisman...named after JOHN Heisman) this is a football/baseball reference? Plus being a coach, as we know Van Pelts father is, you would have to travel around a lot. Could Tigers/Tyger be a sports team?
It has already been mentioned that VP has potential to be seen as easily fooled, she believes in the supernatural, questions Jane, has a hidden/troubled past...a sister who died?

I think VP or someone in the immediate team (Minelli?) could either be the insider or unknowingly helping RJ.

I really hope it doesn't turn out to be PJ in some sort of rubbish 'personality twist' ending. I think this is unlikely.

My other plausible guesses would be Partridge or Kirkland.

No character we have seen in the series is Red John.

This season they have shown us they are pretty much okay with doing flashback episodes that present us with characters that have never appeared on the show before.

All the clues they give, the shaking hands, books and rhymes, it doesn't have had to be shown on the show.
I think they will just keep writing for the character of Red John, completely unrelated to his "real identity".

If the show gets cancelled and they feel like they owe us an episode that concludes everything, they can write Red John in and build a flashback-episode around him and show us 'unseen footage' featuring Red John.

To be hones this a brilliant way to keep the series engaging, one of the worst things that happens to drama series is trying to steer it too much.

Please stop with theory about PJ's double personality!!

-Rosalind should have recognized his voice, his build

-Who saved PJ from fake RJs?

-Lot of people were with him when he was chasing RJ in Mexico

-Lorelai said that he had already met RJ. how did she say so if she knew who RJ is truly?

In this theory there are too many inconsistencies

The theory about Summer as RJ is much more plausible, and that's saying something!!