My choices:
President Richard Adar- He has been through the show "in spirit" from the beginning and Roslin has swore by him basing much of her policies on his. It could deliver the dramatic twist needed. It would make sense why Xena fell to her knees and apologized. (The Cylons destroyed a civilization they already had control of, and possibly their own "plan") Plus it follows all the clues Moore has dropped in interviews. (Known in season one, the last cylon is not in the Last Super shot, ect... ect...) It also shows even a greater betrayal than Baltar.
Tom Zarack- Pretty much for the same reasons I think Adar is the last cylon, but a lighter version. He could have been tortured on New Caprica. (Hence the apology) He has always been in power positions, curving events. The only thing that keeps me saying no, is that he is an obvious choice.
Head Six- I hope Moore does not do this, but I would not put it past him. The last Cylon is a biological program, maybe transmitted by virus. Kinda li9ke the whole thing from terminator III "Skynet is the internet"
