Here's my top suspect list for RJ, after having seen recent episodes, and given all the clues (or red herrings?) we have : 

1) Walter Mashurn : Along with everything other people - and I - have posted before, I just want to add that on the CBS 'Who is RJ' page, he's the ONLY one who really stands out because he's wearing his red turtle neck. Could be a lil sign (or wink, if you will) from the writers to indicate it's him simply bc he's the only one wearing anything red. Know it seems too obvious - but it's like finding Waldo, isn't it? 'Hiding in plain sight,' as one of the writers quoted. And that's what really stood out when I looked at that page. At the same time, it's easy to argue that it's just a coincidence (or herring) or that bc CBS doesn't even know who RJ is (bc they probably don't..) it wasn't intentional. However, that was just a side-note, he is really my top suspect because there is a lot of evidence to back him up in being RJ: personality, narcissism, charm, money, likeability with Jane, 'He is Ma', his love/hate of women and womanizing qualities, the fact that Jane couldn't properly read him, the fact that he has a past with women and his mother, which could explain why he started killing and became what he is... The list is endless, it all fits, he would be a perfect RJ in my opinion. (And how he is the ONLY one we've seen on the show that Lisbon's gotten close with, other than Jane. Which shows similarity with Jane, and advantage he has over Jane: he's slept with her, Jane hasn't. The fact that he's the only one, other than Jane, who's been able to really get close to Lisbon and gain her 'confidence', cannot be a coincidence. If Mashb is RJ he will abuse her trust, and use it against Jane at some point.) 

2) Dean Harken : A lot of little evidence suggested that points towards him, and it would be a cool twist. Would be a sort of 'Ohhhhh yeah, him!' moment when flashbacks of the hints from previous episodes, are shown again. However, a lot would need to be explained - motive, reason for pursuing PJ and women... etc. 

3) CBI Ron : Same. A lot of evidence (especially the Waldo-esque quality of him, always there, in the BG) which would make it an interesting twist if it ended up being him. And the anagram of his name with Red John and Cut Iron is quite clever. However, again, evidence for motive is lacking and would need to be explained. And with Ron, he seems to be a bit too plain and nice to be RJ - don't know if the actor has the talent to pull off RJ and his dark side. 

4) Max Winter : Always been a suspect of mine, even before reading the mentalist 'wikia' page about him. There's just something about him - his coldness, the loss of his wife, the way he sat down just like Jane sipping tea, his calmness (he's TOO calm).. And after having read the wikia page, it's easy to be convinced: finding out that it was in fact RJ who gave Jane the gun to kill the fake-RJ in S3, aka becoming one of RJ's minions through this and doing RJ's job for him without knowing, would be incredible. That's SUCH a manipulative RJ move and it would make a lot of sense. Other details - such as his seeking 'revenge' (mirroring Jane), telling Jane to pursue his quest (showing an understanding of Jane), and his connections, shooting abilities, as well as other little word-hints... It all fits. On the other hand, while it's a very, very plausible theory, the one thing that pulls me back is that all of his similarities with Jane seem to be genuine : as in he really wants Jane to go find the person who ruined Jane's family, and he really seems to want Jane to find redemption. Then again, the actor playing Max is clever and it could all just be a ploy to fool Jane, and throw suspicion off of him. If it's him, I would be pleased, honestly, because the fact that he tricked Jane into doing his own dirty work and taking someone else's life (just like he's made all of his other minions do) without Jane even knowing would be an awesome 'Aha!' moment. It would really show how RJ's truly been one step ahead of Jane the whole time, and how much of a manipulative genius he is. 

5) Ellis Mars : Despite me not liking this theory or me not wanting it to be him, I admit that it's entirely possible. I admit this regretfully, as I don't think the actor can pull off an evil / dark side. (No offense intended, just my personal opinion, ofc!) I admit that him being a 'psychic,' the little 'tiger' on the card he handed out, the 'El es Mar', the 'Elliston farm', these hints all make him a good suspect. And it's true that him acting stupid and ditzy could just be a trick to throw suspicion off himself... At the same time, all the hints with Mars could simply be red herrings or coincidences put to confuse the viewer into thinking it's him. I don't know, with Ron and Mars, I feel like they're just red herrings, and can't really be Red John. However, I've put them on my list because it's still possible, and could make sense, and if it is revealed to be either one of them, I won't be extremely disappointed.  

Which brings us to the people I don't think RJ is (more like the people I hope he's not because IMO it would be a huuuuge let-down) : 

1) Brett P : I know he's a fan favorite, so i don't mean to insult, but my god would it be obvious. 'Oh wow it's him! Yay no element of surprise here, we've kind of basically known all along!' And he doesn't have the presence or the power or the gut to pull off what RJ has - building this community, this undying group of followers around him. If its him, it wouldn't be clever, it wouldn't be surprising, the actor really is a 'ghoul', and a loooooot of explaining would be needed. WHY? Why the target around women? So many questions would need to answered. And honestly, PJ and RJ are supposed to be alike and symmetric in many ways.... How on earth are PJ and Partridge similar? Partridge is just a sad, lonely, spiteful little man with no backbone. Who hates Jane bc Jane's right. I'll stop at that and say that I pray he's just been a red herring all along, because I could seriously go on forever as to why I think and hope he's not RJ... And the fact that he's in the season finale, and other such details, depresses me , so I'm hoping it'll exclude him as RJ , and we'll find out once and for all that he's just been a red herring all along.  

2) Robert K : Ok, seriously, TOO obvious. If the writers make it him, then they're just insulting our intelligence. And they've got a hell of a lot of explaining to do. We've not been following RJ for 5 or so seasons to learn it's him. Would be a joke. There would be no element of surprise at all if it's him. A more interesting theory is if we find out he was actually some sort of 'good guy', like Miranda M's ex who was out to seek vengeance on her killer - which would explain his killing of Lennon even after Lennon said he didn't recognize him, and which would explain his asking if Lennon recognizes him. Would make a lot of sense, and be quite a clever revelation, finding out the guy made out to be so creepy and evil is actually not so bad, and is only seeking his own vengeance against RJ in his own way. I think it's plausible, though there are loopholes such as his RJ-like lingo, 'the plaything of monsters', 'I'm a friend' and the use of the green poison... Either he's seeking vengeance , or he's one of RJ's minions/accomplices who will eventually get killed off. But please, writers, don't take the easy, unoriginal way out and make him RJ. Would be such a horrible, unsurprising disappointment. 

3) Ray Heffner, Royston Daniel, and others : All possible, but probably just coincidental red herrings. Still possible, but vey unlikely. 

Ok, there you go: my full list of suspects and anti-suspects! Just threw it out there to see what people think, how many people agree and disagree.