Yandere Kanojo is pretty good in that respect. Also, it's questionable if she's the female lead or if she's stronger than the main character, but Ryoko from Angel Densetsu is really strong throughout the series.
I also love manga with strong female characters, so here are some of my suggestions:
- Skip Beat! - Joou no Hana - Akatsuki no Yona - Maeuigeom - Pharaoh's Concubine - Soredemo Sekai wa Utsukushii - Chang Ge Xing - Koushaku Reijou no Tashinami - E? Heibon Desu yo?? - Jigoku no Enra - Kamisama Hajimemashita - Tianmei de Yaohen - Cheonsaeng Yeonbun - My Dear Cold-Blooded King - Isanghago Aleumdaun - Prince, Don't Do This! - Hadashi de Bara wo Fume - Kaichou wa Maid-sama! - Miunohri to Swan - Love in the Mask - Crash! - Queen Regnant of Heaven - School at Imperial Court - Aoi Horus no Hitomi (Dansou no Joou no Monogatari) - Ao Haru Ride - Mairunovich