Haruna - fan of Korean music, self-professed lover of TVXQ (DBSK for some), and erm..Justin Bieber
Tomomi - err, I forgot, but she loved Judy and Mary IIRC, then again, so does most of the band members. AFAIK, she got inspired to play the bass after watching Flea from Red Hot Chilli Peppers in a concert DVD.
Mami - Likes Aiko, among others, and is generally attracted to bands with great guitarists.
Rina - Err, I saw her with a The Who album before, and she likes Maximum the Hormone, and her first karaoke song was Otsuka Ai's Kingyo Hanabi. She listens to YUKI too from what I can see.
Basically the girls listen to a lotttt of music, same with me, I don't think I can write down all of the artists I like properly xD