Though, let's think this through, people:
* The final Cylon is not one of the main characters.
* S/he was not "triggered" by "All Along The Watchtower."
* S/he would not have been aboard the
Galactica when the activation occurred, the way Tigh, Tyrol, Anders, and Tory were.
* This probably means s/he was always aware of what s/he was.
* Which makes him/her the "control" Cylon. The only one who really knows what's truly going on.
Taking the above into account, the final Cylon has to be someone whose inner thoughts, whose psyche, hasn't truly been revealed to the audience. S/he also has to be good at manipulating people. And it'd have to be someone who was off-ship when the activation happened, and who likewise wouldn't have been "summoned" to the room where the revelation occurred.
It's Romo Lampkin.
Remember too, Ron Moore insists none one of the main characters are the final Cylon:
"Moore swears it isn't one of the show's primary humans. Not Starbuck or President Roslin. Not Admiral Adama (Edward James Olmos) or his son, Lee (Jamie Bamber). Or even the ever-dubious, Cylon-shagging Gaius Baltar (James Callis)" [Michael Ausiello, TVGuide.com].
They are feinting too much for Kara to be a Cylon, so she's been run through the wringer, but is still human. Of course, since a major part of the show is paranoia over who's a Cylon, simply having a final, unrevealed model is crucial to the dynamic, even if it turns out to be Bob from Accounting.
Also, Romo himself allegedly had a wife and two daughters, and the series has established that Cylons can procreate with humans when "love" is present. And the Final Five can even procreate with other Cylons, unlike the seven known GenoCylon models.
Tom Zarek is my other pick for the Final Model, as he fits exactly the same criteria, but based on what we're hearing about the new
Caprica series, there's apparently an established, known Zarek family lineage already present in the Colonies, unless the Tom we know on BSG is some sort of clone of an original Tom Zarek.