Kirsten Dunst has a naturally round face and both of these hairstyles work well on her, although I prefer the right, longer hairstyle on her. I feel it makes her round face appear less round.
Why the left hairstyle works on Dunst: Bobs are usually a no-no on round faces because they can accentuate the roundness of a face, but you can get away with a piece-y long bob, as Dunst does here. Make sure the bob hits at least a couple inches below the chin and make sure it's styled imprecisely. For inspiration, check out this photo gallery of long bob hairstyles.
Why the right hairstyle works on Dunst: Again, length is key. Long hair elongates a round face and the way the hair falls like a curtain, it hides some of the softness of Dunst's face. You have a million long hair options for your round face. See Long Hair: My Favorite Long Hairstyle Photos for ideas that fit your hair texture.
Not all short haircuts look bad on round faces. Read on for ones that do...