Google Image Search (using the phrase "most beautiful woman in the world") says it's Aishwarya Rai.And if Google says it, it must be right! All Hail Google!
kim is all types of gorgeous.
Oh, I have just found out that the answer is Kithara. How silly of me not to know this.
I don't think there's such thing as THE most beautiful woman in the world. Even if you find a 99% acurate example of the perfect ideal of beauty (that's also different depending on where in the world you are) say in the western cultures, I'm totally sure you can also find more women matching that criteria. And even more: I'm sure you can find many other women who DON'T meet those beautiful standards, yet they look even more attractive than the first ones. Perfection is boring.