Naoko & Momoe
One of Naoko's favourite singers is Yamaguchi Momoe, so quite a few times in the past, Naoko could perform Momoe's hit songs during her live performances. Here are two:
http://rapidshare.de/files/3519327/yumesaki_annai.wmv.html
http://rapidshare.de/files/3519630/yokosuka_story.wmv.html