Gene theraphy with viral vectors. That area is still on diapers, but has a massive potential. It could be used to cure any genetic anormality. No one will suffer again of Insulin Dependent Diabetes, or Galactosemia, or any of those nasty Glicogen storage diseases.
Another one, although it sounds more like science fiction, is 3d printing tissues. We would be able to built skin grafts or muscle grafts from scratch, or even a kidney (lets fantazise a little bit).