Amamiya in
Psyren has a pretty tough/stubborn/cold personality, and most of the female cast in this manga are pretty tough.
the females in
Jormungand and
Ordinary, and I mean ALL of them, have dark personalities if not tough. Well, they're all either weapon smugglers or mercenaries or assassins for hire.
Black Lagoon is pretty similar to the two aforementioned works
also, the female cast in
Doubt (TONOGAI Yoshiki) are definitely dark if not borderline evil (but that's also a spoiler). they are not that tough, though.
I don't know if
Claymore fits or not because though they're strong, the female protagonists seem to have some sense of justice and good, so not exactly dark
several girls in
Narutaru get pretty psychotic later on and had somewhat dark personalities to begin with
Tista in the manga
Tista is an assassin. Sometimes she is depicted as dark/psychotic (well, almost)
Anne Freaks - the female protagonist is pretty dark/calculating