stars (male/female tradeoff poppy/sappy love songs ((i only have in our bedroom after the war, its very good)))
seconding warpaint/tilly and the wall/the knife
ghost mice [folk punk, forget her name but she sings on most songs. male/female duo]
this bike is a pipe bomb [folk punk, same stuff. little easier on the ears than ghost mice]
nana grizol/defiance, ohio - more folk punk/folk rock stuff, not really female fronted but ladies sing a couple songs/verses here and there, music is great too, some of my favorites. i would check them out regardless
matt & kim [great poppy duo]
danger mouse + daniele luppi have a pretty cool album out "rome"
CSS/cansei de ser sexy - poppy dance music, some cool music videos. [ http://www.youtube.com/watch?v=7agPOt1XZz8&ob=av3e
idk. looking through my library i dont have many strictly female leads/singers besides things that i feel are probably too obvious to mention but most of the above minus the folk punk ones are probably in that same category of obvious [yeah yeah yeahs/rilo kiley/regina spektor/the fiery furnaces/eisley].
long list but definitely get stars, matt & kim, the wreckers if you can only grab 3
then grab the nana grizol/defiance, ohio ones just because they are awesome as fuck female leads or not