After the last episode I got confirmation to a thought of mine. Red John isn't a single person. All the 7 people on the list are parts of the Red John persona. The last one(s) who'll stay alive by the end of season will be the brain(s). As we've seen Partridge cited from W.Blake. And the psychological description of RJ contained traits of all of the ones who were alive.
I know we've only seen him in one episode, but I think it could be Danny Ruskin, Jane's brother-in-law.
I was thinking and I realised that RJ seems to know a lot about Jane's past, indicating that he may have been involved in it somehow and at first I thought Jane may have a brother or sister that we've never met, but that would be rather disappointing, wouldn't it? But what if it was his wife's brother?
In the one episode we see him in (Cackle-bladder Blood), we learn that Danny grew up on the same carnival as Jane and that he later became a con-man. This would explain why RJ knows so much about Jane's past.
We also learn that Danny dislikes Jane a lot for two reasons, taking his sister out of his life and then for getting her killed by taunting RJ on TV.
But really, Danny didn't seem like the kind of person who would do that. He is a con-man though. He could hide things well. Maybe he thought that if he couldn't have his sister in his life, neither could Jane. And maybe his hostility isn't towards Jane getting his family killed, maybe he hates him because he taunted him on live TV?
Anyway, I did a little research and I found out three interesting things.
1) When people leave the carnival they don't get to come back. People hate it when others leave and the phrase 'dead to me' is often used. I know this isn't substantial evidence or anything, I just thought it was interesting and maybe a small hint at who RJ is.
2) This point is a lot more interesting. We all know how RJ uses the alias Roy Tagliaferro. Well the name Roy means red. and Ruskin has the meaning 'red-haired'. We know from Jane that people tend to use aliases that are similar or have a connection to their name.
3) After reading about the Roy-Ruskin-Red connection, I decided to see if Daniel and John had any connection at all. The name John means 'God is my judge' and the name Daniel means 'God is gracious'. I know this isn't a very definite connection, but if RJ is at all religious, it could be a possibility.
Also, remember how 'RJ' told Jane how Angela smelled before she died. Well it was done with a car bomb, so it's likely that he wouldn't have come close enough to her to know that. But someone who grew up around Angela would maybe have memories of her perfume how she would often smell.
Danny also fits the physical description of RJ very closely. The actor, Kevin Rankin, is 1.82m tall which is 5 feet 11 and 21/32 inches (points to google calculator) or just under 6 feet? We also know that he is younger than Angela (his sister), but he can't be much younger as he isn't much younger than Jane. His voice also fits the description of RJ's;soft and high-pitched.
Finally, in the same episode we meet him, Jane describes him as a 'sociopath, like all good con-men' and he often describes RJ as a sociopath too. So, does Jane maybe secretly know in his mind, as we know that RJ can hypnotise Jane?
So yeah, that's my theory on RJ being Danny Ruskin.