Eyes(not so much color, although I do have a thing for blue and green eyes), the shape but especially how expressive they are, the look in them.
What really makes someone beautiful, is the way their personality manifests on the outside. Some people have this natural elegance about themselves, partly a physical thing and partly from the inside, a reflection of who they are. I also find it beautiful when a person "feels" nice and trustworthy, I guess it's tied with charisma.

There is a type of physical build (in many variations according to stature for ex)that I usually find more attractive than the rest, naturally athletic I call it, not the pumped up at the gym type but rather the build of someone who exercises for fun and health.

Other than that, physically, I can find all sorts of features and combinations of features, beautiful.

I have a thing for voices as well, the type of voice Hugo Weaving ,Hugh Laurie, Alan Rickman have.