The Whispers
Not sure if this has been said before, but I've got an idea about the Whispers. I definitely think the series is heading for a loop. Basically, I think the Survivors will al be re-united somewhere near September 21,2004, and they'll realize that they're all coming back on the 22nd. Then, they would know everything that happened, and would know from either Ben, Richard or Jacob, that the Whispers were actually the Time Flash Survivors checking in on their future (or past) selves.
If I remember correctly, the first time we heard the Whispers was when Sayid escaped from Rousseau. Time Flash Sayid would know, "Hey, today's the day I escape from Rousseau." He would go out to where he heard the Whispers and whisper to make sure Crash Sayid heard …