Libby theory:
Libby was on the bridge that Hurley made collapse, killing all the people, she was not injured but a good friend was killed making her “crazy” (which is why she was in the asylum with Hurley) until she snaps out of it only for the revenge of getting Hurley back. Following Hurley to Astralia and back to only crash on the island.
or
Libby is a “gold digger” and knows that Hurley is a filthy bastard and has been following him.
or
It’s just a conincidenc ethat she was at one time “crazy”
or she is part of the Dharma project and was hired to follow Hurley and get him to the island.
The two people that will die by the end of the season (reported by the producers).
Jack. Abrams will get to finally kill him off since he couldn’t in the first episode. Which makes me think his back story has nothing to do with the main plot since he was going to die in the first place. He’s also getting to get on peoples nerves lately the same way Shannon and her brother did. The craziness of late could be attributed to the disease though. It just seems there is something wrong with him.
Charlie. Another character that is just getting on peoples nerves and he seems to have found a little redemption with Ecko which might make his death heart-felt.
Libby. Just a possibility since Hurley’s getting a little close and the island doesn’t like new love. ie Syid and the Shannon.
Anna Lucia. Every one’s been saying she is to go but the producers said that they made her character the abrasive type to only peel it away later and I haven’t seen that at all and I actually want to see her character develop into something other then what she is. It’s been brought up that she will go since she has to go to jail. It’s only for a week and it’s happening now I believe or close to it.
 What brought down the plane.
The magnetic machine or whatever you want to call it split the plane in two, knocked everyone out and then safely placed everyone and the plane on the island. The flying ghost things are also controlled by magnets and they were used to wake everyone up by blowing the engines up and such (which is an actual occurrence in episode one if you slow-mo the part where the engine blows).
Walt could be possibly involved.
 Him?
Locks dad is Him.
Well, I’ve already posted a couple times about my Libby theories, so I won’t repeat those here.
I actually had thought about Jack dying too, for the same reason.
I am going to predict that Charlie will not die.
I am going out on a limb and predicting that Desmond is really whacked out when he comes back, possibly from going through withdrawals, and ends up killing one of the losties.
From the preview for the next new ep., it looks like “Henry” attacks Ana Lucia, and it wouldn’t be a huge surprise to me if he kills her then. I think that would be a great way to do it, if it’s going to be her. Apparently unlike almost everyone else, I actually liked her character up until the point where the two groups were reunited.
Until that point, I think she played the intended role well (showing how vastly different a perspective one group can have than another, even in relatively the same circumstances, and the varying degree of effectiveness of their responses based on that perspective). Tragically, though, shooting Shannon was the last interesting thing she did, and from that point on, she has easily been the most boring character in the series, for me at least.