Red John / Roy Tagliaferro is Brett Partridge.

First I will begin saying why others suspects aren't Red John.

- All female characthers are excluded: Kristina Frye, Grace Van Pelt and other womans. ( Red John is male, all clues indicate that, the big one is when all Red John's  accomplices are talking about RJ with "he" "him"

- Main Characthers: Like - Patrick Jane, Teresa Lisbon, Van Pelt, Cho , Rigsby -> are not Red John by many reasons but I will just name one of them. -> They play on all episodes from The Mentalist show, Red John is someone hidden and someone which hasn't appeared on all episodes.

- Bret Stiles : He is not RJ! Why? As You know... Patrick Jane is very smart, maybe more smart than you think. In one episode with Visualize, Patrick Jane had a conversation with Stiles and he told him "You couldn't hurt a fly". If Patrick felt that way about Stiles, he was definitely sure. Stiles is harmless, he can't be a cold blood serial killer. Second, Stiles is too old and from my opinion, Bret Stiles know who Red John is, but he won't tell Patrick because he is afraid of Red John not to kill him. I expect on next episodes / season the murdered of  Stiles by Red John.

CBI Bosses - Gale Bertram / Virgil Minelli : Alot of theories about these guys, but they are wrong. Noone of them fits the profile we allready know about RJ, described by the blind woman.

Robert Kirkland, Ray Haffner and Ellis Mars - Even they fit RJ profile, noone of them is Red John, they are just suspects placed on the show by Bruno Heller for us, to disoriented the audience.  There is have to be alot of Red John suspects, so thats why we have them! RobertK is very interesting, he plays his role very well and mysterious, by the evidence, he can easy be a RJ accomplice.
Lorelai told Jane, he and RJ shook hands, and one episode later, Jane and Robert are doing this thing, WAKE UP people, is just a TRAP placed very well by the creator :)

CBI RON - If you look careful at Red John's appearance, you can easy say that he can't be Red John, because he is to "fat" in the first place, and second, He doesn't fit the profile of Red John, Rosalind haven't described Red John to have a beard + mustache.

Walter Mushburn: "Unlimited $, intrigued by murder" and "PLAYBOY" he likes to play with everyone, is open, and he act like he doesn't cares about nothing, his play on the show indicate that he doesn't hide anything.

Now I present my theory about Red John being Brett Partridge:

He fits perfectly the profile!
Stop sayng he is to young, he isn't, Brett Partridge is 44-45 years old. He is perfectly old enough.
His voice is identical with Red John's voice -> http://www.youtube.com/watch?v=7rjXOkCxUUw
His act, How we play on the show, is perfect for a cold blood serial killer, which is tryng to hide his tru identity against Patrick Jane.
You can see Red John's ( Brett Partridge ) face right here !
https://www.google.at/search?hl=de&q=janet+peak+brett+partridge&psj=1&bav=on.2,or.r_cp.r_qf.&b...=&u..........

Brett Partridge and Patrick jane they shook hands, ( offscreen ofcourse ) because you can see his name on Patrick's notebook -> http://www.google.ro/search?hl=ro&site=imghp&tbm=isch&source=hp&biw=1280&bih=709&q=brett+partridge&o........
why do you think Patrick described Partridge in his notebook "TOTALLY MACABRE" ? because he read him
IF you watch many times, all scenes with Brett Patridge and Patrick Jane, I repeat many times...and you are a good face reader ( like "Lie to me" :D ) then you can definitely see the fear from Partridge face when we talks with Patrick , ESPECIALLY! when he pronounced Red John words. "Ok... so where is Red John?" 
Watch careful his fingers and shoe size and then compare it with Red John, they both fit perfectly.
We know that Red John got spanish friends, this means Red John know to talk spanish: -> "Que pasa dude?" "Amigo"
 On 2x23 - Watch the first scene with Brett Partridge and Jane, after they talk, Jane leaves the room , leaving Brett alone, then suddenly he comes back and scares Patridge, and this was more an arrogance act from Jane. Later on the episode when is the scene beetwen Jane and Red John, EXACTLY the same thing has happened, Red John leaves, Patrick is tryng to calm down and then suddenly Red John comes back and scares Patrick , the same "mind trick" Janes has done to Brett Patridge.

I've got one more thing to share with You before I end my theory. And I really would like to see comments about this.

We see Brett Partridge again on S5x15 ( again.. he is tryng to induce in error Patrick about the murder investigation like allways ) 
( by the way in this episode you can see exactly the size of shoes and fingers from Brett Partridge and then compare them with Red John , you will be surprised, like I said..)
Okay...What I wanted to say is, when Brett is talking with Cho about "his theory" Patrick Jane is looking around on the room, he heads to a table with books (Many RED books also..) There are 17 books and 7 books are written by Rex Stout and rest of them by others authors
7 books by Rex Stout -> R E D J O H N , a book for each letter.

RED JOHN: Tyger Tyger, burning bright 
                     in the forests of the night
                     what immortal hand or eye
                     could frame thy fearful symmetry 

PATRICK JANE (different episode): When you see the face you feel fear!

What am I saying, well notice the final line of the poem 'FEARFUL SYMMETRY'. How about this, if the face represents fear then 'symmetry' symbolises the general symmetry of the face e.g. the circular motion of the face. Then note the third line of the poem spoken by Red John, where the words immortal hand are used. This basically suggests that all though Red John is not immortal the smiley face and the fear he will leave behind long after his death will be immortal. And the word hand means of course the hand he uses to craft the face. 
The key word in the poem is SYMMETRY. Now this is the important bit, in the Pilot episode when we are first introduced to Brett Partridge he talks about the crime scene, but it is not his words that are important it is his action and the camera shot that are the important part. The camera is placed directly behind him and focuses on his hand as he uses three fingers to imitate the outline of the face on the wall. Brett uses three fingers to represent the perfect SYMMETRY of the Red John smiley face.
So in conclusion Patrick says when you see the face you feel FEAR, and Brett uses perfect SYMMETRY of his fingers to represent the face. Thus being FEARFUL SYMMETRY. 

Kirkland is introduced in the show in Red Dawn as “the man in
the limo”, which means that he started getting interested/involved in the Red
John case exactly the same time as Jane joining the CBI. He then appears when
Lorelei breaks out of prison and when she hunts for RJ.

It wasn’t necessary to actually involve himself directly in
the case before that, because he had already arranged for Jane not to be able
to interview Lorelei. When Jane/Stiles broke her out of prison, Lorelei became
a potential threat to RJ because he must have known that Jane might be able to
get to her in some way and turn her against him.

So, as far as we know now Kirkland could be RJ himself or a right
hand man. Point is, that RJ either had to get his own hands dirty or send
someone more higher up the chain to resolve the mess Lorelei made. This means
that RJ actually raised the stakes of the mindgames he is playing with Patrick
by giving him a night with Lorelei as a gift and nearly lost all when Patrick
got to her. Things may look like Jane lost another round in the RJ game, but
this time it is more or less even. I’m sure he made RJ sweat a little for the
first time.

I think RJ may start to feel that he should be more careful
if he wants to keep winning. The problem with gambling is that it’s all about
loosing…

okay, so clearly Robert Kirkland is an interesting character. But I don't think he is RJ just for the fact that you don't make your big mystery nemesis so obviously suspicious. He is important though. If it was chess, then RJ would be king and RK would in my opinion be the queen. 

I suspect this because for starters it is clear there is a connection between RK and RJ. Also RK is in a high and powerful position. This means he has power(duh..), but this also means that he is smart, purposeful, and that he gets the job done. If i were RJ then i would definitely want this guy as my right hand. Besides this he enters the story at a convenient time. The story needs someone more interesting than all the minions that represented RJ till now, so they trow in someone high up the food chain. like in a game you face a sub-boss before fighting the real boss. that is the function of RK in my opinion.

For RJ himself I think he hasn't entered the story yet as a purposeful character  For me with all of the first 10 suspects I understand why he/she could be RJ but it would always be kind of a disappointment, like a cheap trick. I hope in the end it will be more complicated then 'taadaa, it's the CSI guy' or 'haha, got you, it's grace'. Till now RJ has some screen time I think, but more like a suspect in some case, or a witness or something like that. So if you find an actor with a too high profile for a 50-seconds role, then in this theory it would be plausible that is RJ.

but heck, what do I know. Maybe it's still a a dream in the end, and RJ is actually PJ's father!

(off-topic)I read somewhere that at times that RK is present that there is RJ-related background music. didn't check if that's true but it would be interesting to find that kind of patterns with certain characters.