Massive Dexter fan here, and I must admit I joined this board just to participate in this discussion, since I've been trying to type the characters for a while. I'm still fairly new to this typing thing so some of the arguments go over my head, but I'm willing to learn.
Thank you similutedworld for your post - awesome - but it also raised a few questions for me.
Firstly, I find it interesting that so many of the PD characters are typed as Ns - Doakes, Deb, Harry, Maria, Masuka and Dexter himself. The last three I agree with completely, but I'm not so sure about the first three. Simply because, from what I've read, most police officers are Ss. But perhaps its their iNtuition that has elevated these characters from typically S uniformed positions to the more N-like detective work.
Doakes is the main one I'm thinking about. Can someone tell me why he wouldn't be ISTP? Because his preferred mode - lone wolf, not bound by convention, free to take risks - seems like classic SP to me. Plus, I would imagine that a Black Ops operator, working mostly on his own like he did, would basically describe an ISTP. He doesn't seem meticulous enough to be INTJ, for mine. Sure, he certainly uses his intuition in suspecting Dexter as a bad guy, but it's based on his own experiences - what he has observed in Black Ops - not some NT-like reasoning of "research shows this is what bad guys are like".
On the other hand, if Deb is an S she'd have to be ESFJ, because the E, F and J are all obvious with her. And I can't see her as an ESFJ - not traditional enough - not really the motherly, dinner-party-organiser type. Plus, it's probably her N-ness that enables Maria to eventually (grudgingly) respect her as a detective. As an NT myself (like Maria), I reserve particular snobbery towards Ss who miss my intellectual point. :o. But I do think Deb might be losing some of her Judging nature, especially in season 3 with her relationship with Anton. (For Dexter's sake, he'd have to hope she becomes a bit more P or else she may turn him into a punching bag when she finds out Rudy was his brother.)
Plus, I still think Dexter is INTJ. He may be becoming more INFJ, but the majority of his decisions, including the decisions about whom he is going to kill, are made using T, not F. The times when he's exercised F in decision-making (whacking Paul with skillet, headbutting Doakes, doing risky stuff with Lila, stabbing Hicks when he insulted Rita) have been exceptions, not norms for him. His natural sociopathic side - his Dark Passenger - may be more F, but he is able to control that part of him mostly.
Finally, been trying to type a couple of the minor season 3 characters.
I'm thinking Ellen Wolf as an ENTP - typical defence lawyer, flexible, can take a hard-arse approach when needed, doesn't particularly care whether her clients are innocent or not, just whether she can succeed in her defence of them. She also displays what could be seen as "masculine" type tendencies regarding her sexual relationships. But she has strong F characteristics, as shown by her willingness to help others, so she'd be borderline ENFP.
Sylvia - ESFJ? I think she's pretty similar to Rita - which explains why they get on - but more extraverted (would need to be in her job).