Pretty much album of hers has classics:
...Baby One More Time - ...Baby One More Time
Oops! I Did It Again - Oops! I Did It Again, Lucky, Stronger (arguably)
Britney - I'm A Slave 4 U, I'm Not a Girl Not Yet a Woman
In the Zone - Toxic
Blackout - Gimme More (the intro alone has become part of pop culture)
Circus - Womanizer, Circus
Femme Fatale - Till the World Ends (debatably), Hold It Against Me (debatably)
Britney Jean -