Except from the description details by Rosalind harker Reede Smith is the most plausible because if you switch the alphabets you would got "the red is me".

something that bothers me is when jane find out that someone enter in his "office" (the lirlkand mens) he wasn't angry or worry he smile.
well it dosnt matter now becouse it was before patrick finish the list 
my theory about who might rj be is that not ether  bret stiles (he is old and dont have the  physical fitness) or bertram(he dosnt match with the description of rj girlfriend) are red john. however i think that  both are accomplices of red john.
now that i remember agent smith from the fbi is not red john becouse of the rj girlfriend description

Not saying it's him, but check out Reede Smiths face expression starting at about 1:12 when Rigsby says "We were this close to catching Red John before you blew it."  

I wouldn't say he is red john, but a good friend of red john is likely.

http://www.youtube.com/watch?v=I_s2oCpsneE

Obviously there is no way to be completely sure, every character has done and said a million things that make him or her just as likely to be red john. But Im going to assume Heller isnt being tricky when he says RJ is one of the 7. He says we will be disappointed when we find out, and Reede would be ver very disappointing because his role in the show is so small. Also, rearrange the letters in his name and it spells "The Red is me." Finally, the only episode he appears in is titled, "The Crimson Ticket." Remember when RJ has Jane and he says Roll Tide? Well the Crimson Tide of Alabama use that slogan, and the ticket thing sounds like a football reference. But I can make strong cases for Partridge and Van Pelt as well, so who knows!?!?!?!?!

It's him !
I'm pretty sure off that!!

What do you think about that ?