I'd be extraordinarily surprised if Bush renominates O'Connor.
Two things: first, O'Connor has not resigned. She has announced that she plans to resign pending replacement. She is still on the court.
Second: contrary to what many here have said I think this is good news for the liberals. It is going to be much harder work to confirm two of what the media will call "conservatives" (Roberts and one other who may actually be conservative). And the talk of Chief Justice Scalia or Thomas? I really don't think so. That would mean three confirmation hearings fighting against Chuck and the RINOs. Hope I'm wrong.