This is more a summary of my top suspects 

-Brett Partridge: There is a lot of good evidence supporting him as RJ. Some may argue he is too young, but that is not the case. I won't rehash what evidence has already been said but I will add that in the pilot when Jane is describing why it isn't RJ, Partridge looks very uncomfortable and we assume it's because he is getting called out by Jane. But if he is in fact RJ his discomfort can be explained in that he is surprised how well Jane understands him. Thus this moment is the start of RJ's liking toward Jane.

-Redshirt guy- The guy in the finale of S3.

-CBI Ron He's in the background, always there, we don't know much about him. Very well could be RJ.

-Kristina Frye- She is my oldest suspect so I have a hard time dropping her. While everything is making it almost certain RJ is a man, if the writer's throw in some kind of twist that could explain RJ being a woman, then it's K Frye for sure.

My other explanation would be
-RJ is 2 people (not an entire organization: This would clarify the rape of Lorelei's sister (I don't believe RJ would rape a victim)
-The writer's will throw in some curve about RJ when he is revealed that will be impossible for any of us to have predicted (like RJ is some long lost brother)

Who RJ is NOT
-Robert Kirkland
-Roy Haffner

I don't know why so many theories point to these guys just because they were made to look like suspects in recent episodes. The Mentalist never has the obvious person as the culprit. For example, S3 finale, of the 5 suspects, LaRoche and Bertram were the ones made to look like RJ's man, but neither were. Also see every other episode of The Mentalist ever for proof of this.

It is now concrete, although obviously was that RJ was or is connected with visualize. I mean when you listen to Lorelei speak about him and how he was able to help her set herself free...visualize crapola talk...like all religious cults. So RJ was a kid working on a farm where he was training to be a killer by first mutilating animals...then killing his first 2 victims in that basement in the barn.  Leaving his smiley face mark for all to see...he is not in the CBI...he isn't Kirkland...so this is how this season ends...Volker works a deal because he probably knows who RJ is...we get very close or maybe even see RJ as he is in the finale..RJ kills Volker...then dissapears...just seconds before Lisbon and Jane make it to stop anything.. Kirkland goes to prison...and that ends S5...still nothing resolved...except now we know who it is...but he will be untouchable till the middle of next season where Jane will have to figure out someone kind of manipulation to bring him back into the light...

The first clue he is man...clearly meant to be he is many otherwise why on earth wouldn't he just write out the name. A couple of other people have mentioned the cult being murderers. I think its unlikely the whole cult is in on it. That would be impossible to hide. But its very obvious from various episodes that red john is mentoring serial killers through an organization. So I think brett stiles is definitely in on it. Also a coincidence that bret partridge has same name.. how many people are called bret! The two are clearly linked to red john and yet neither has shook Jane's hand. I think the theory that Brett knows red john is clear perhaps even schooled him. The whole business of red mist and cleansing yourself its an easy leap to think brett stiles has developed an ideology that consists of murder as being a rite of passage. Add in the poem of lion taking his rightful place amongst the lamb.
So visualise is involved its likely brett knows who it is via the cameras that record everyones secrets but would rj wouldnt be that stupid. But brett has to be involved he is the only person with that amount of clout. I think it may be the guy who tried to stage a coo in Visualise. He drinks tea, has shook janes hand and fits the description. The voice is an issue but lets face it that's probably put on. Either that or what about that creepy little guy who gives jane a globe reading he appears in a couple of other episodes and his voice is pretty creepy. Also the most hilarious part is there is a lawyer in visualise called john.. XD
In terms of end theory bruno heller wants to get another two seasons out of this so, i think at least for season 5 we'll probably catch somebody. Either van pelt shows different colours or jane finally finds out that theres a network of serial killers...also jane is not red john that would be beyond stupid and totally implausible. 

Hello everyone. This is Andre_John again, and once again I'm making a theory based on Brett Partridge as RJI also made other theory's that you can read here on Bret Partridge (one of those got 89 plausibles and 5 unlikely's) and also on CBI Ron.

So this time let's add some science to the investigation, which means MATHS. (I know, boring, but easy stuff, I promise)

Alright, so in the last episode we learned that RJ worked in a farm in the date of 1988.So assuming that we are in 2012 in the show:
2012 - 1988 = 24

So, we know for sure that RJ has 24 years at least.But we also know that the workers in that farm started with an age between 16 years and 23.
So let's say that RJ was really young and started with 16:
24 + 16 = 40.
But I think that for a first murder, 16 is not likely, so let's say he had 20.
24 + 20 = 44

Okay, so let's consider that RJ is now 44 years old, more or less.
I always thought Brett Partridge was RJ or in some way, one os his puppets. But I thought, well Brett seems a little bit young to me, like 30 years or around that,but we have no idea about his age.So I went googling on Jack Plotnick (Brett Partridge actor) and he is exactly 44 years old.

So, Brett is RJ or maybe one of his puppets. About that I'm 100% sure.

Along with Brett Partridge I think there are some other possibilitys that fit in RJ age, but two of them are most likely:

1- CBI Ron (My favourite suspect. Maybe he is RJ and Partridge works to him), and as we know he is getting more and more importance in the show. In the last episode he gives Lisbon "Happy Birthday!"

2- Virgil Minelli.

There are also some other clues like Ellis Mars ore Mashburn, but I think that Brett Partridge, CBI Ron, and Minelli are the most likely.
Thanks for the attention once again.