The more I think about it, the more I believe that, what's going to happen is there is actually two more cylon's. One is part of the final five, the other one will be the one original cylon or at the very least (as mentioned in another post) the puppet master (so to speak). I think the reveal of the last one of the final five will be a bit of a surprise but not a real shocker either. The big shocker will come when they arrive on earth, and the real final one (The 13th one) will be waiting for them there. And I also believe that the 13th will be a major character who gets killed during the season or has already been killed. And the series will end with them saying something like " Welcome Home" or something to that effect, leaving the door open for a motion picture or whatever.
To tell you the truth I don't think that would be a bad way to end it. I think it would definitly make us crave for a motion picture, or very much, look forward to " Caprica" to see how and why this person came to be.
This is just a theory but who knows,
Anything is possible in RDM's world.
Hmmm, what's that ? Lunch, maybe..?
F**K it, I'll eat it anyways !!!