I dont think its  Bob Kirkland because Bruno Heller said that everybody will be surprised once when we find out who he is. Your really think he would make it this simple ? Bob kirkland may be helping red john, but i dont think he is red john himself. 

Robert "Bob" Kirkland is Red John!
When he first met Patrick Jane they shook hands. And only after that episode, Lorelei told Jane that she's surprised they didn't become friends from the moment they shook hands.
Furthermore, he appears out of nowhere into the center of the RJ case, and seems to control some of the most powerful figures (Virgil Minelli).
In my opinion, he is too involved in this case, being just a recurring character.

we know Bertram is working with RJ because he asked Kirkland if Lisbon can be trusted (another suspect of mine) but if you listen carefully in the season 4 finale, when RJ says "you strung me along a good long while, well done" he sounds almost exactly like Bertram  but I don't believe the show would use a character as big as him, and he just doesn't fit the expectations for RJ. he is defiantly an accomplice.

After last nights episode, we know that Bertram is at least working for Red John.

He is a white male
He is not fat or buff
He has easy access to PJ
He wants to know PJ's theories
He sook hands with PJ
He once called PJ the boy wonder ( PJs stage name) which is strange because PJ is a man
He used a William Blake poem.

Maybe it's Bertram.

I am sure it is Virgil Minelli.
Miranda was killed with a fishersman's hook, and Minelli has been seen fishing after his retirement. The 5x16 character Jason Lennon(the RJ accomplice from the shelter) was also a fishermen, and tied Miranda with fishline. Minelli and Lennon met during fishing and became friends.

For me it's sure that Red John is Minelli!