Damon Lindelof and Carlton Cuse reveal: nothing, they just tease us: "Let's just say the end of the season features a showdown between Jack and Locke — a showdown long anticipated and a showdown with an extremely significant outcome for the future of the castaways." However they do say: "I think Penny and Desmond's relationship will become something that will be a part of the season finale."
Edward Kitsis and Adam Horowitz reveal that Hurley will be playing a central part in the Finale.
Kristen E!Online: ''The game-changer involves Jack and someone else. A fan favorite will sacrifice himself for the good of the rest of the Losties.'', '' The casting call for the final two hours of season three includes a single mother, a doctor, a mortician, a pharmacist and a stewardess. The pharmacist and the stewardess are hardasses, the doc is a chief-of-staff, the single mother is tired and the mortician is kind of depressed.'' Harold Perrinaeu will not be back for the Finale however the producers wanted him back for the Finale.
Media Week - On still-mysterious Lost, no season-finale is complete without someone dying. Who that will be is still anyone's guess. The survivors of Flight 815 will have another showdown with the "Others," the origins of the Dharma Initiative will be explained, and the beach occupants divide into two camps: one run by Jack (Matthew Fox) and the other Sawyer (Josh Holloway). One old face you will not be seeing is Harold Perrineau as Michael, who actually turned down an opportunity to return in the season finale. At this point, we have to assume that Michael and Walt are safe and sound at home.