Ismene

I think Ismene is a good complement to her sister.  While Antigone seems to have inherited Oedipus'  willingness to act, and his passion, Ismene seems more cautious.  In the story so far, she looks like she is just very submissive and people could walk all over her.  However, I think she is merely more thoughtful, and more likely to think of the consequences of her (or her sister's) actions.  To me, this quote sums it up very well:

"Antigone! Dear sister! Think how hated out father was when he died. How full of shame! ... Then she, who bore the double name of mother and wife, took her own life with a rope.  Then our poor brothers perished in the one day, each of them killing the other with his own hand.  And so, now we two are left alone.  Think what awful end we can expect if we go against Creon's law! ... To act beyond your ability is mindless folly."

She is trying to dissuade Antigone from doing this by telling her what will happen if she is caught. Unfortunately, it didn't work, and only made Antigone mad.