I don't think there's a bat's chance in hell Merc will take him. I thought McLaren (minus the PR days) would be a great choice for him, but hiring Kimi would be tantamount to the always-politically-correct McLaren saying Kimi is better than Button (not that I would argue). Ferrari paid him off for 17 million or something, so fat chance. Renault's Kubica seat is a far shot, though I'd love to see him there.
Maybe Raikkonen replacing Webber though? I think it would be good for Red Bull and Vettel's image; if Vettel were to consistently beat, or at least equal, someone of Raikkonen's talent.