[Z-man]

When Diana was unboxed, and she had a conversation with President Roslyn, she clearly said that FOUR of the final FIVE are with the fleet. Unless she was lying, that would mean the following folks cannot be the final cylon:
- Baltar
- Starbuck
- Adama
- Anyone else aboard the rag-tag fleet.

Thus, I think the final cylon may be one of these folks:
- Billy, Presiden't Roslyn's first political advisor
- Ellen, Col. Tigh's wife.
- President Roslyn's Spiritual advisor, who was killed on Kobol.

Personally, I think it is Billy. If Dianna was lying, then I'd bet it is Zarek, the current VP (played by Richard Hatch)

-Z-man.