I had a bit of a think for this one as my first instinct was to write Natalie Portman... but I do think her beauty kind of has an impact so purely on talent... I am going to say Renee Zellweger (and yes, I did have to look up the spelling before typing that!).
She is an incredible actress in everything I have seen her in, and she is so believable at each role she plays. I think it is also really amazing that she put on weight and managed a very convincing British accent for Bridget Jones's diary!
She is great and I hope the rumours that a 3rd Bridget Jones film is in the making are true!