Hey, I'm bringing this thread alive again because I just finished watching season 4.
My take on the final cylon:
Here's my case for Starbuck:
One clue is the whole sequence when Starbuck comes back and the fleet is jumping off course from Earth and she's going absolutely nuts. Throughout these episodes and on the Demetrius she kept on alluding to the fact that her understanding of where earth was was strongest when the fleet was back at the nebula..... Precisely the geographical point when Tigh, Tory, Sam and Galen heard the music and eventually found each other.
Remember that conversation that Starbuck had with Admiral Adama in the first ep of season 4 when Adama asked her to tell him how does she knows the way to earth? She told him 'It's a feeling, an intuition". How did the cylons find their way to that room that revealed their identities in the first place? How did they find their way to the hangar and to Starbucks' ship in the final ep? Well I'm pretty sure they followed their feelings and intuition without understanding why they knew that info, just like Starbuck.
My final point takes place in the final episode where all 4 cylons heard the music once again which lead 3 of them to the hangar and to Starbucks' vyper. It's my belief that it took the 5th cylon to find out 'what's changed' on the vyper which evidently became the final key to earth.
It would explain why Leoben and Sam Anders are so attracted and devoted to her. Because of her special destiny, and perhaps because of their subconscious feeling that this is the 5th cylon.
As a footnote, I found this webpage where this dude describes the 12 cylons as part of 12 archetypes representative of the basic human needs, aspirations, and motivations. Here's what he came up with how starbuck fit into the 12:
THE EXPLORER/SEEKER/WANDERER= Starbuck (if she is the other cylon)
The Explorer/Seeker/Wanderer leaves the known to discover and explore the unknown. This inner rugged individual braves loneliness and isolation to seek out new paths. Often oppositional, this iconoclastic archetype helps us discover our uniqueness, our perspectives, and our callings.
http://forums.nightly.net/index.php?showtopic=48467