I think judge Manchester is very likely to be red john...he easily has the power, money and influence for all this...also, something is seriously cookin in that poker group...
In season 1 episode 11, jared renfrew writes "he is man.." on the wall....dat could be manchester,...
also, in the same episode at the very end, red john calls jane and laughs....if we hear the laugh of manchester during the poker game in season 5 episode 14, its the SAME laugh....
One more thing...wen bosco was in charge of the red john case, red john kills him to give the case back to jane.....now in season 5, judge manchester effectively does the same when the case is almost taken by FBI....

I do not think Patrick Jane is Red John. BUT I do think that the writers have tried to point some evidence towards him being RJ just to manipulate the viewer. And they have succeeded, obviously.

The reason why I believe that in the end Jane is not going to be revealed to be RJ is simply because it's a tv show, not a (M.Night Shyamalan :p ) movie. That means that there's way too much material to cover at the end, when trying to tie all the knots together and prove that RJ and PJ are one and same person. To satisfy the hard-core vigilant fans, they would have to pretty much reshoot every scene in the series where PJ and RJ are interacting with one another, or where RJ's accomplices act nonchalant to PJ's presence to explain what has actually happened, and why they are acting like they are. And that would make the story line and ending way too messy and over-blown to be good tv. In a movie this would naturally work, because there'd be way less material  to cover in the ending revelation.

Another reason why I think PJ is not going to be revealed to be RJ is, that I think the Mentalist is  a classical "Superhero" story where Patrick Jane is the hero and Red John is the nemesis. Sort of like a Batman and Joker kind of a scenario. The story is enjoyable because it shows a hero "good" character slowly descending in to acts that are nearly equally evil as the nemesis' acts, in the name of catching the "bad" guy. I think this story line works better with the series.

I also believe that Patrick Jane does know Red John personally or at least knows something about Red John that he's not aware of. I think he's under hypnosis, and I think the mental institution where he was is the place where he first met RJ personally/was hypnotized. As PJ's IMDB Trivia page says, all the close-up scenes with PJ show his pupils dialated, which supports the theory of him being under hypnosis.

I do think that the creators have been toying with the idea of PJ being RJ, and in a way that would make a clever plot twist, though hard to execute. That would also explain why the RJ smiley face looks like PJ (c'mon, it does, doesn't it?). But I think it's more plausible that PJ is, without being aware of it himself, somehow helping RJ or feeding him information/being in close contact with him. And I think Lisbon is going to play a role shaking him out of the hypnosis (or whatever) in the end.

Thanks for taking the time to read.

I perceive Red John as a subtle, calm, patient, cautious man, and maniac in the way that detail is very important to him.
I would be disappointed in finding out that Partridge is in fact RJ, because he's seems to be a simple-minded fellow. And the way he jumped in to defend the killer when Jane said it clearly couldn't have been RJ proves to me that he is an unlikely candidate.
Mashburn... eh. No. Why would two women of the show be sleeping with RJ and his affiliates?
Bret Stiles? Doesn't seem likely to me. I can't defend myself on this point, but it wouldn't surprise us enough, I think.
"Hiding in plain sight", I interpret it more like this - we see him, someone may have already spoken to him a few times, but I don't think he's been major and present all along.
But that's just my theory, I'll remain humble.