If there are three deaths coming up and assuming that the one last night wasn't included in the number, I'm thinking Bonnie, Alric (sp), and Matt or Caroline's mother.
I think they foreshadowed Bonnie's death last night when she told Jeremy about what using all of the dead witches' power would do to her, with Alric I can see him sacrificing himself or something to stop Klaus, and with Matt he's been abused so much its about time to put him out of his misery. I also don't see who Caroline's mother can go on now that she knows the truth.
I don't think Klaus will die, it seems like he can possess bodies so it makes him extremely hard to kill. Any 'death' would be temporary.
Of my picks, I'm hoping Bonnie will pull through. She's hot and I would like to see them develop her relationship with Jeremy.