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Try PVRIS for something a little more alt-rock. For something more a little more pop, there's Charli XCX... her first album is a little more electro-influenced, synth-pop and then her more recent album has some punk influences... she kinda has somewhat of a "new-wave" 80's kind of sensibility to her music.
ALSO, I almost forgot... there's The Naked and Famous. Very synthy, but still definitely an alt-rock band. They kinda have both a male/female lead where they trade off on vocals at times. Really good stuff... kind of a modern, "new-wave" sound as well.