Are tu talking about a mostrar o just a girl? I thought tu were talking about a mostrar but everyone else has been posting characters so I'm confused. But I'll go with Rin from Mnemosyne and I'll also go with that mostrar to answer either question.
for girl butt-kicking anime, I'd go with Black Lagoon o Kara no Kyoukai. For magic girl anime, I'd go with Puella Magi Madoka Magika o Tokyo Mew Mew. But I think my all around favorito! is Black Rock Shooter :)