I Think there are many many possibilities 
Including 
Bret stiles
Walter mashburn
Gale Bertram
Virgil Minnelli
Bob Kirkland
Jj laroche
Brett partridge
But one that not many think of... Janes Father, im unsure of his whereabouts and if he is still alive or not, but jane did walk out on him in the show business, it makes sense, he would have know patrick well before he started his murders, Im quite muddled on dates and what not but that is my theory

Nobody is yet RJ. The movie is made to keep us in front of the tv's for years. So, at the begin, it was just a motive to put a criminal like this in a story,like the bad guy. We are now at season 5 and RJ didn't appear in way.The makers of this movie created a site like this one, www.whoisredjohn.com for us to say our opinion because lot of the characters can be RJ. Now we are voting for who is RJ :D And I assume that it will not be the one with the most votes on this site, because it must be a surprise.In the end the idea is cool,the create a site to see the people's opinion and after that to create who is RJ- like this: RJ is in ours minds and now we are creating it on this site

I think it could be Tolman Bunting from the episode, 18-5-4 . He is the one that runs a puzzle store as well as a security firm looking for a code breaker device to read encrypted files. He is caucasian, little less than six feet tall, short hair, slim build, not a deep voice, not quite high pitched but more nasal. Is intelligent, manipulative, knows computer systems, could easily or have someone hack into CBI and/or police computer systems. He enjoyed playing a chess game with Jane, so is competitive, perhaps a sign of enjoying cat and mouse games. What do you think? 

its hard not to think there are multiple suspects working together on behalf of red john. heller is really good at manipulating the situation to make us think it is one man (which i believe it is) but since there are so many theories pointing to multiple people, the easy conclusion is that they work together and cover up for one another. and they are all around patrick all the time. I think as the series unfolds in the next few years jane will start unlocking the pieces of RJ's network and it will really start looking like individual red johns are exposed only to uncover another piece of the puzzle with a dramatic climax at the end of this show.

*Bertram and LaRoche laughing at a poem by william blake together (not even a funny poem either). LaRoche also killing the suspect that had a tie to red john. Bertram personally walking jane to the mall to meet the supposed red john. Minelli gives him a list of suspects made by LaRoche. how the heck did he get a little piece of paper from LaRoche's pocket that no one else saw unless its just a rouge to throw Patrick off? Minelli keeping ties to alexa shulz and the man in the seat with her (kirkland).

was O'Laughlin the mole or was it really Hightower and he tried to kill her. it could still be Ardiles who set johnson on fire. He's still on the suspect list. Jane seems to always help Red John followers around him thinking he can help them, but hightower could definately be one of them. she has a tie by her former lover being murdered by a disciple.
i wouldnt rule out one of the immediate team members being a disciple either, especially VanPelt and her ties to Stiles now, and that Stiles personally knows red john.

Weird things..... the "He Is Mar" thing... the "r" in the writing looks exactly like the "i" in "Is" but because of the angle of the half dead girl writing it falls at the end. that could throw off all those theories but i could be wrong. One last crazy thing... before Jane turns the page in his little black suspect book there is one name on the other page on the left that has notes under it and the others dont. I think they did it on purpose, but i cant slow my media player down enough to make out the last name. The first name is SAMMY  and i cant see the last. it has two lines of notes and one line i can make out says CHANGE.. if anyone can get that info please let me know.. 

all that said i believe RJ is a law enforcement officer who has most of the poeple do the killing for him. 

I've seen lots of people blame Marshall cause he's name start with "mar", the theoretic sentence we saw on a episode where 2 guys got killed in Mexico. If you look at the episode 1x20 you can see that the agant Marshall opens the car's door with the left hand which is pretty unusual if you look at the position he's goin (min 14:509 and we all know that Red John is left-handed (we see that when Rosaline calls Jane and John is in the background with a couple of tea) I don't know if Marshall is Red John because i personaly belive that the sentence wasn't "Mar.." but something like "na..", but i think my particualr support those theories that hink Marshall is RJ. Thanks

Dr Roy Carmen- s02/2/02 9:33min -listen to his voice!! and his name Roy- everyone who know Red John called him "Roy"...

After watching and loving this show, I had an epiphany. Who has Jane hurt in the past and carries a grudge. Who wants to test him, as he did in the past? At the same time, who cares enough about him not to just kill him? Who believes in his talents enough to push him and taunt him for the slights he feels Jane caused him? Who did Jane walk away from, setting this all in motion to `teach him a lesson' in who was smarter?

His father.

Red John is Jane's father.

Side Note: Has anyone noticed that the smiley Red John paints on the wall looks a lot like Jane when he smiles? Just a thought