1) Jennifer Garner
2) Jodi Foster
Many of her roles are those of the ordinary woman who finds herself in an extraordinary postion. Think of Panic Room and The Brave One.
3) Kate Beckinsale
She has a gentle, beautiful face but think of the two Underworld movies - tough and invincible.
She has dreamy eyes that express depth and vulnerability but she is tough at the core. Think of The Day the Earth Stood Still and Blood Diamond.
Think of the Terminator movies, especially the second. Who can dispute that she was one of the toughest heroines yet.
There are of course many others, and I'm sure I will use them in the future to create variety, but for now these are my five.
By the way I have my three book covers over on Book Cover Lovers: http://bookcoverlovers.blogspot.com/