Natalie Portman and Catherine Zeta-Jones are the two that instantly spring to mind for me.
Judy Holliday beating Gloria Swanson and Bette Davis is beyond my comprehension.
This was what Davis had to say about the result:
"I wouldn't have minded losing the Oscar to Swanson if she'd won for Sunset Boulevard - coming back after all those years, playing a woman that she must have known well. Aries or not, Swanson was very special.
But to lose to Judy Holliday, that was a shocker."