Ok, this was written after having seen up through 3x06.
Dexter--At first, ridiculously INTJ. Almost a caricature of INTJ--a brilliant, creative and rational thinker whose very existence is dependent upon introverting his thoughts--cool, calculated, methodical, tidy to the point of OCD, and at times emotionally retarded. In fact, if you want to understand the INTJ type this is the perfect character for it. The entire series is basically about Dexter's development from a total INTJ into more of an INFJ.
Deb--ENFJ. Can be pushy and a bit stubborn (J), but ultimately lives to serve others in a grand, far-reaching kind of way (NF) and is extremely extraverted to the point of sometimes being obnoxious, contradicting her F nature. As Dexter points out in the very first episode, she is "the only one that really loves [him.]" She's a bit prone to simply declaring (J) what's best for others (E) and then refusing to change her mind, but usually has honest and good intentions (F), and is typically right in these predictions--classic ENFJ.
Rita--ISFJ. Caring, traditionalist, selfless, loving mother type who finds her purpose in providing for the specific (S) needs of others (F) in an organized and consistent way (J). She tends to be rather private and takes time to let others in (I), but possesses an extremely high sense of duty toward her loved ones and can always be depended upon in others' times of need. ISFJs often have problems with being assertive or sticking up for their own abilities even when they know they deserve to be recognized--as such, they are sometimes under-appreciated. This leads to Rita's ongoing struggle to learn these assertive social skills throughout the series.
Harry--INFJ? This one is tough, but I think it makes sense that Deb grew up so much like her father--as NFs, they are drawn toward service to the community (Harry's personal bitterness over various guilty felons who went free leads him to justify his cultivation of Dexter's serial killing tendencies to himself by declaring that he is "channeling [Dexter's urge to kill] for good the greater good"--a classic NF justification.) Seems to make this judgment rather quickly when he discovers his foster son's true nature, and then is very methodical in devising (N) and carrying out plans (J) to train Dexter to keep his true self a secret. INFJs often fantasize about "getting back at" those who they see as taking advantage of the weak or downtrodden, and are often champions of "the little guy." When he finally walks in on Dexter mutilating a victim, he is so overwhelmed with guilt at what he has created (F) that he commits suicide. And all the while his concern for Dexter's well-being is one of his biggest motivations (F), but we're left to decide for ourselves just how much he was driven by desire for revenge/vindication of his own failures. Very interesting character.
LaGuerta--Easily ENTJ. A strong, opinionated and outwardly focused (E) rational thinker not particularly concerned with the feelings of others (T) who's not afraid to use unconventional (and sometimes arguably unethical) means (N) in her own meticulously crafted plans (J) to advance her career.
Doakes--INTJ; the NTJ similarities explain why he and LaGuerta were first attracted to each other, and also why their relationship failed. Another strong rational thinker (T) who ignores conventions in creating (N) and methodically executing (J) his own plans without regard to the established methods (N), rather than enforcing traditional rules (as the ESTJ tends to do) and is often excessively controlling, blunt and assertive (J) with little to no regard for others' feelings (T.) This also explains why Doakes sees through Dexter's social mask so easily--INTJs are known for their lack of social interaction (I) and terrible emotional intelligence--and as much as they hate each other, these two are very similar.
Angel--ESFP, as the type that lives most fundamentally for the present-moment, tangible experiences of right now (SP), Angel is friendly and loves to party (E)--he is constantly out at the bar, trying to pick up women, but is driven by a very deep desire to help and serve the specific needs (SF) of his coworkers, and is often guilt-ridden when he fails. He feels intense guilt over the failure of his marriage (F) and often gives in too easily to his impulses and the opinions of others (this P-flexibility allows LaGuerta's assertive ENTJ influence to impact his professional decisions, for instance.)
Masuka--ESTP, fundamentally an outspoken performer who has a deep need for the approval of his peers. As an SP, he is over-the-top, persuasive (maybe not as much as he thinks), and sometimes downright obnoxious. In a never-ending attempt to garner attention and entertain his "audience", he is constantly cracking some ridiculous and often offensive joke but seems too oblivious to the feelings and sentiments of others to notice that it's not always appreciated. I like how in season 3 he grows into a real dynamic character instead of just continuing to be a stereotype.
Lundy--ENFP-- He is driven by a desire to "fight evil" (a very NF characteristic) and feels compelled to do service to the world through his work. He is also generally warm, compassionate and open to new leads and ideas, but can wear himself a little thin through his constant efforts to save the world. These qualities, combined with his brilliant intuition for criminal investigation, catch Deb off guard and lead her to falling in love with him. She eventually becomes disinterested as his strong P function leads him to "spread his love around" a lot (sooo NFP!) and often precludes him from making serious long-term commitments.
Lila--ESTP, attention-craving, present-focused concrete thinker (S) who ignores traditional rules and seems to thrive on acting on impulse (P), Lila is highly proficient at manipulating others (E) for rational self-gain, and has little concern for the feelings of others (T).
Paul--ESTJ, overbearing macho type, but feels a sense of duty to uphold tradition (SJ), as evidenced by his one redeeming quality: his commitment to helping raise his children as well as he can after his initial release from prison.
Miguel (new character in season 3)--ENFJ, he is a brilliant, creative and association-oriented thinker (N), which combines with his F function to place him in the NF temperament--he is drawn to service the community (F) in an outwardly focused (E) and methodical (J) manner. As the season progresses his NFJ desire to punish the wicked for the greater good of mankind begins to overtake his entire moral worldview.
Joey (new character in season 3)--ISFP, seems to be a pretty concrete thinker (S) who's not afraid to switch up his approach and step outside the accepted method (P). Often acts on impulses and gut feelings. Also seems to have a particular gift with understanding the emotions and needs of others, but it has been suggested by Yuki that he is more self-serving than he appears to be. May later change to ISTP after more data. Interestingly, he has only one trait (F) in common with Deb, but her flair for intuitive planning (NJ) seems to reflect and compliment his impulsive SP behavior and disregard for rules and regulations.
Ramón (new character in season 3)--ESTP, feels a strong sense of duty to avenge his brother's death but is very short-sighted and can't seem to keep his anger and aggression in check. Often overbearing, controlling and insensitive (T) as he forces himself into the investigation, feeling increasingly helpless to do anything about it. Seems to believe he can simply
convince the Miami PD to do a better job of finding Freebo--always the salesman.
Anton (new character in season 3)--ENTP, smooth and confident smart ass (hence the song he plays for her at the bar) who can't help but push the limits (i.e. lighting the joint when Deb threatens to arrest him.) Nonetheless he is impressed by her spirit and intrigued by her conviction, and begins to open up to her after their first unfortunately negative run-in.
Yuki (new character in season 3)--Not much data yet, seems pretty ENTx in her articulate, sardonic style of speech. We'll see what happens with her.
Rita's Mother--Stereotypical ESTJ female--traditional, authoritarian, stern and even sometimes cold (T), exceedingly controlling and easily offended when her value system is challenged, especially by one seen as "below" her level of authority.
Interesting that I only profiled 17 characters and came out with 11 different types as a result. I suspect that good character interaction results at least partially from having a wide variety of character types at work.
(By amusing coincidence Joey (I
SF
P) and Ramón (E
ST
P) came out right next to each other in the list. And who's the consummate SP?? Why, none other than Joey Ramone, of course!)
The missing types seem to be:
ISTJ--I'm sure there's some minor character that's ISTJ and isn't noticed, for just that reason.

ESFJ--Eh, maybe that lady at work that Dexter gives donuts to?
ISTP--Not sure if such a character will come up; Joey may turn out to be one after all.
INTP--Interesting that there's not one on the Miami PD staff...could be a good addition for future seasons, maybe a rival blood spatter analyst?
INFP--Would probably play some kind of supportive character role as like...I dunno, a girl whose life Dexter accidentally saves after killing her asshole overbearing ESTJ boyfriend?? One can only hope ^_^