You should definitely check out Tokyo Jihen. While they are rock, and pop, its usually a mix. Their first album is more rock, their second album is like rock jazz, and their newest album is more pop/rock. So I guess if you are looking for pop, check out their newer album, Variety. They are fronted by Shiina Ringo who was also a solo artist. Check out their wiki here:
http://wiki.theppn.org/Tokyo_Jihen