Looking at this from 20000 feet...
You are creating a TV show whose hero is a crime-fighting fake mentalist who
believes all spiritualism/religion is humbug - you're GOT TO to make his
protagonist a believer/religionist/spiritualist/otherworldly-power-summoner.
And Mr. Heller did. The dinner conversation in the 1st episode between
Jane & Van Pelt wonderfully showcased the humbug vs believer tension and
set down the anticipated premise of the show.As a TV show creator you MIGHT put "false" clues in your show (like the stretch in an early season where seemingly every other show
had a mugshot of someone who was 5' 11'). You MIGHT even spread "false" rumors
about your show (like the list of 7 Red John Suspects).But you DON'T make Jane's protagonist some obscure sheriff from Napa-Sonoma-Wherever who has no particular spiritual angle/connection.

Now that we're orirented we can start looking at clues.

The REAL short list of susects is:

 Grace Van Pelt
  - has cousin who is real psychic,
  - feels kingdom of God is a very real place
  - based on dealings with Stiles, seems attracted
    to spiriual like moth to flame
 Theresa Lisbon
  - always wears cricifix
  - meetings with Jane in church
Brett Stilles 
  - Visualize conectionLongshot candidates:
 Kristina Frye  
  - spiritualist/mentalist
Ray Haffner
  - Visualize conection

To me, Van Pelt is the most compelling, so I won't be saying a lot about the others. Van Pelt's position at CBI lets her keep tabs on Jane, gives her access to useful
information, and allows her to manipulate siuations.

How hard is it to access Patrick Jane's private thoughts - the ones he's never told anybody? Its EASY if your cousin is a REAL psychic

Wait you say, Red John is a man right? "John" is a mans name, and a woman
wouldn't have a mans name, right?  Well people who might have known Red John describe
a man with female-ish atributes.

In any case, who's to say how manly Van Pelt is? Her former fiancee? He's dead.
Wayne Rigsby? In the latest episode he bluts out that they haven't yet had sex. When
he adds "as a married couple" is he clarifiing a mis-speak, or obfuscating a truth that escaped unedited. Not sure.

Did someone try to warn us of a female Red John in a previous episode when they tried
to write "sHE IS MAn"as thier dying act. Only to have it get smudged?

After the last episodes trench coat scene I'm looking forward to Cho and Rigsby's weekly talk about whether Rigsby and Van Pelt are "doing it". Should be an enlightening moment
of truth for these speculations. It might just put 'em to rest. Or confirm them.

Don't need em though. How do we know for SURE that the person Rosalind Harker knew
was Red John and not an associate.

Need more clues? Check out the obligatoty word/letter cipher clue:
   Red John = Cvc Cvcc = Van Pelt
The vowels and consonants match! (sorry I had to do that, but "It's the Law")

Oh yeah and she has red hair.

I rest my case.