Joan Jett, Susanna Hoffs and Cheryl Cole have always been the biggest for me.
Some other musicians I've found especially attractive are Siobhan Fahey (of Bananarama), all the Spice Girls except for Baby (no slam, she's just not to my tastes), Debbie Harry, Madonna, Kylie and Danni Minogue, Pixie Lott, Nelly Furtado, Agnetha Fältskog from ABBA, Ariana Grande and Billie Piper.