If you haven't already heard of Lykke Li, then you have to also check out her first album, "Youth Novels." Every song on the album is excellent, it's hard to pick a favorite. "Time Flies" is a great slow song and "Breaking It Up" is a good upbeat song.
My new favorite girl artist is Jessica Lea Mayfield. If the Black Keys support this singer/songwriter then so do I! I first heard about her from the Spin SXSW artists article and then literally a week later she was the free song of the week on iTunes, which was frustrating because I had just purchased the same song! Anyways, she just released a new album, "Tell Me." I love the songs "Kiss Me Again," "Call Me," and "Our Heart Our Wrong."
Definitely check out Jessica's new album. She is also featured on the Black Keys' song "Things Ain't Like They Used To Be."