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They are called the Secret Sisters. They are relatively young, and are just starting to blow up. T-Bone Burnett has produced some of their work, and has really helped them. That link is to a song titled, "Tomorrow Will be Kinder" that just so happens to be on the soundtrack of that movie from the books everyone seems to like, Hunger Games.
They are really doing well for themselves. I read in the paper today, that they will be on the debut episod of a new concert series show that will be airing this Saturday night on APT (check your local listings ). The show is called Front Row Center.