Raised by Another/Daddy
Apart from all the other daddy issues:
Ok, Charlie is on the fast track to being "daddy" to Claire's baby, though the bio-daddy is back in Oz.
There are hints (swollen feet, for one) that Shannon may be knocked up, either by her Ozzie ex or by Boone. And Sayid's likely to be the "daddy" there. Unless she gets killed first (ok, so I'm insanely jealous. He's mine, darnit!)
Though there have been no hints, Sun may be pregnant as well, and Jin's so ticked off at her he may not want to have anything to do with her or her baby leaving Michael to step in.
Locke was raised by foster parents.
Sawyer was raised by others (not sure if relatives or foster system) after his parents' murder/suicide.