316 Theories
I think that certain people must have known that Oceanic Flight 815 was going to fly through the island window and these people made sure that certain people were on that flight so that the island could bring them to the island.
Jack's grandfather says that one of these days he's actually going to get away from the home and they won't ever find him. I think he knows about the island, and that's where he would go if he got away.
As much as I don't want it to be true, I think Ben went to the marina to kill Penny. He told Charles he was going to, and when he saw Desmond, he knew that Penny must be nearby.
Who is the man who gave his condolences to Jack as he walked away from the airline ticket counter? We also saw him on the plane? I think he's going to end up on the island too. I think the island wants him for something.
I think Hurley might be on the plane because Charlie told him to go and also told him to take one of his guitars (though I can't think of why the guitar would need to go other than the fact that there was a guitar on the original flight).
The island wants Jack to read the note from Locke, which is why he can't get rid of it.
On the plane, they saw the light and heard the humming sound and then they were suddenly on the island. Jack, Kate, and Hurley don't remember the crash. I don't think the plane crashed, I think the island pulled the people it wanted to the island and the rest went on their way. Which means more than the Oceanic 6 could have gone to the island and the island may not have wanted Ben.
Observations from 316
Eloise tells Jack to start thinking about whether or not he thinks the plan to get back to the island is going to work. "That's why it's called a leap of faith, Jack." As we've seen in the past, Jack has been a man of science. Here in the future, though, he has been much more of a man of faith.
When we first see Christian walking around the island, he is wearing a suit and a pair of white tennis shoes. After he'd died, Jack put the tennis shoes on him, thinking that no one would see his feet, so that he would be ready for the funeral as soon as he got back to L.A.
Ben tells Jack that Locke's body is at Simon's Butcher Shop, which is the butcher shop that Charlie's father, Simon, owned.
Jack listed Locke's body as Jeremy Bentham rather than John Locke.
Lost fan noniflower points out that when Jack asks Ben how he can read, Ben says, "My mother taught me." But Ben's mother died just after he was born.