Elizabeth Bennett (Pride and Prejudice): My favorite Austen heroine, and definitely one of my favorite heroines. I love her wittiness, her sarcasm, and the fact that she makes mistakes when judging people. ;) I also like how she tries to take care of her family despite their various idiocies/eccentricities. Plus she eventually has the good sense to fall in love with Mr. Darcy, who is just awesome!
Jo March (Little Women): I just read Little Women this last year and REALLY identified with Jo. I know a LOT of girls do, but...yeah! That's why she's classic and timeless! So many of her specific little problems are things I have struggled with or am struggling with.
Jane Eyre (Jane Eyre): She does what she believes to be right, sticks to her guns, puts her foot down, whatever expression you want to use. I think she's amazing.
Flora Post (Cold Comfort Farm): This girl makes me laugh out loud. She knows what she wants, by thunder, and she WILL make it happen, no matter what obstacles fall in her path. But I also love that she learns to adjust her goals (not too much, just a little) if things don't go completely the way she wants them. But in general, her plans go through.
Eowyn (The Lord of the Rings): She's kickack, loves horses, marries Faramir, kills a Nazgul, fights for her loved ones, and learns that gentleness is as pwnsome as awesome sword skills.
Leia Organa (Star Wars): Childhood hero, WHAT CAN I SAY? I love her snark and her good looks and her diplomacy and her "Someone has to save our skins!"
Lucy Pevensie (Chronicles of Narnia): She's innocent, brave, faithful, kind, and faith-full. Possibly the Mary Sue of children's lit, but I love her.
Sophie Hatter (Howl's Moving Castle): I have to include her. I love her gung-ho attitude but that she "lacks method." I love her snark, her grouchiness, her stubborness, and her hardcore loyalty and love. When I am an old lady, I will attempt to attain her awesomeness.
Mary Russell (Laurie R King's Holmes and Russel series): She's such a girl of the twenties. Snarky (I sense a theme), courageous, incredibly intelligent, and doesn't take no shill from anyone.
Harriet the Spy (Harriet the Spy): One of my favorite kids books and kid heroines. :) Harriet is curious about everything and doesn't worry what people think of her. She can be rude, but she can also be kind, and is very observant and intelligent for her age.