I like a woman to dress with some sense of fashion and have an ability to coordinate a look. I also value femininity over fashion when it comes right down to the wire.
Someone mentioned sundresses, and I agree completely! For instance, in the first shot below, the above-the-knee flared hemline gives her a playful, sexy look in how she dresses, which makes her appear more approachable (whether or not that's actually true is another matter).
I love denim, a white top and heels! One of my very favorite looks! (Add a Fedora or Trilby for an extra 100 points!) I also like women who can pull off wearing men's clothing. I think it can actually accentuate femininity, especially if she plays up other more feminine aspects of her appearance, like the shot of the woman in the tweed jacket and tie near the bottom of the set of images, with her long, flowing hair.
And then there's always the beautiful Barbara Stanwyck, the last photo in the set. I love the simple lines of her satin gown--sexy as can be. And as Barbara herself demonstrates, there's nothing more sexy a woman can wear than a great smile!