Eyes. Forget the "windows to the soul" crap - that is fairly irrelevant. But a pretty, clear, sparkling pair of eyes is a winner in my book, closely followed by slender and elegant hands.
The first impression thing comes up a lot. Having checked around my friends, of various levels of both playerhood and overt masculinity, I'd say there is one thing that shines out as the most attractive feature a woman can have.
It is not only hugely appealing, but the biggest turn on for men that you can imagine.