Actually, I think Red John is Grace Van Pelt.
First of all, it is more than obvious, that it is someone from inside. I am pointing at the team. Think about it! She's obviously smart, she seems to have a "moral agenda". - Red John has been starring at us from the beginning. Plus, none of the characters, backgrounds have been developed. The killer's trademark is a crying-smiling face. That would hint to someone obvious! If I remember correctly, in an episode Patrick, suggests that Wayne is going to invite Grace, to sleep with him. Afterwards Patrick said, Grace already prepared an answer. My question is, how did she figure out Wayne's intention - she did, because she is a mentalist.
Think about Red John's modus operandi. At first, you see the "art" and afterwards, the murder. I think we are seeing the crying-smiling face at the moment. We haven't looked at the actual murder.