The Bettys

The Bettys is a popular chick rock band that Stacy Hirano and Candace Flynn are fans of.

The band seems to be a parody of the pop rock band based an Australian band called The Veronicas (both of which are parodies of Archie comics characters, Betty and Veronica). It also seems to be based on Spice Girls, an all-female British band. They sing the song "Ready For the Bettys" in the Phineas and Ferb episode of the same name