So I can't believe no one has mentioned Zwei!
Zwei is one of the best J-girl-rock bands ever, imho
They are made up of two girls, Megu (bass) and Ayumu (vocals), and they're just awesome
Ayumu has some of the best vocals in J-pop/rock, not to mention she's one of the hottest tomboys!
They have 2 full-length studio albums, Pretty Queen and Z, and 5 singles. Check them out if you haven't already!
Btw, in the pic, Megu is the blonde one and Ayumu is the one with the shades^^