Psych has a fandom. I'm not sure how large it is, but I remember seeing fic recommendations for it go by on my LJ friendslist (I think it may have been a Crack Van fandom for a while, but I might be wrong). The big thing I don't understand about what I've seen of the fandom is that there's very little Gus/Shaun. The big slash pairing is Shaun/Carlton Lassiter.