Okay Firstly I'm going to rule a few people out..

1. Patrick Jane - It can't possibly be patrick because he was on the tv show the night his wife and child died.. also in the last ep of season 2, patrick is not talking to himself, red john is, and also if patrick was red john, wouldn't timothy carter recognise him, when they're speaking together?

2. CBI Ron - Although CBI Ron is a really good suspect, he can't possibly be red john, because in the episode where one of the office ladies in the CBI kills all the members of the team that were on the red john case at the time (not patrick's team) and she gets sent to jail.. and as she's being escorted by Cho and Rigsby along the prison corridor, a man passes in prison guard uniform and the lady smiles at him and recognises him because he's rj, and he squirts some posion on her hand and she dies.. but if that was CBI Ron, Cho and Rigsby would've said "hi" or something, or would've at least acknowledged him as he was walking past..

2. Wayne Rigsby - It can't be Rigsby, because the director has shown too much of his personal side, being a caring father and all, and the director is trying to make Red John look like a cold blooded killer, not someone who is kind and caring..

3. Cho - It's not Cho, same reason as for Rigsby, the director shows too much of his personal side, ie. his realationship with Summer, which shows he is caring and viewers just wouldn't be satisfied if they found out that a crazy serial killer was just a nice guy..

I reckon it's a relative of Brett Stiles. It can't possibly be stiles, because Stiles is just an Old man, he's not strong enough to pull off murders like that, but I do believe that it is a relative of Stiles' because he would fit RJ's age group, plus last episode, it was said that Stiles bought a whole dozen farms, and who better to get to work on a farm, then you're own son?

Anyway I'm probably wrong, but it's up to you to believe what you want :)

New suspect!! Marshall, Summer´s new fiance.

remember 1 clue was: "he was mar.." marshall fits this and all the other clues given by rosalind.
his face seems familiar cause i´m pretty sure it has already appeared in other episode and maybe he shake hands with patrick!! (so if you have previous episodes: go look for him!! -couse i don´t have them :( - if you find him: you have found RedJhon!! :D

By the way, and according to what lorelei told jane:
1. patrick himself cannot be red jhon (because he and RJ have shaken hands,and this can´t be done with oneself)
2. RJ can´t be any other of his CBI friends (namely: vanpelt, risgby, cho, lisbon)

I've been looking at some of the theories around 'He is Mar' and the only think I could think of is that RJ is facially disfigured or deformed in some way eg he has a missing arm which would set him apart.

1. mar - a mark or flaw that spoils the appearance of something (especially on a person's body); "a facial blemish"
blemish, defect
2. mar - destroy or injure severely; "mutilated bodies"
mutilate, maim - injure or wound seriously and leave permanent disfiguration or mutilation; "people were maimed by the explosion"

I think it is Viktor Rq Hultgren. He is evil and he nurtures from peoples fear

The man who offered Lisbon a new job is red John, he is trying to take Janes best friend and co worker away from him, he doesn't like Jane but credits his intelligence just like red john

Complete speculative guess. I only suggest it because I've not seen it mentioned, and I expect the reveal will be more intricate and fulfilling than how I lay this out but my general assumption is:

John Rubinstein (Judge Manchester)

1)Manchester - football team - nicknamed the red devils
2)' he is ma'.... 'he is manchester

various plot points from episode 14 in season 5 could be red herrings or legitimate clues.
 
3)The first card in the poker game is ACE of HEARTS.
4)Lisbon:" the action is on you judge"
5)Judge:"...like a childrens book....goodnight moon" - http://en.wikipedia.org/wiki/Goodnight_Moon

It's Ray Haffner. It makes complete sense. I mean, think about it. Red John killed somebody at a farm operated by visualise. That was probably his first murder, and he was probably 20. It's been 30 years since that roughly, and Patrick Jane has shaken hands with Haffner. Haffner is a member of visualize, and makes complete sense. He denied the topic when Lisbon brought it up. He pretends to be awkward, but we all know he really isn't. 
There is little doubt in my mind he is Red John.