Newcomers

Emeka: Played by Adewale Akinnuoye-Agbaje. Was reported as "suddenly showing up on the island" which could mean three things
1) Deja vu on the Ethan thing.
2) He's a tail-section guy.
3) He's a rest-of-the-plane nobody.
Also, Emeka is a nickname of the Ibo name Chukwuemeka which means "God has done great"
Ana Lucia: Played by Michelle Rodriguez. She looks familiar, I know. She's the girl from a bar in Jack's flashback. She wound up the tail section of the plane, (which was hypothesized by me), is somewhere else on the island.
Libby: Played by Cynthia Watros. Her character was a therapist—that is—before she was "Lost". Jennifer Jason Leigh just missed the job, before it was snagged by Watros.