For me, its hard to find any woman beautiful. I guess to me, the few i do have what i call an inner glow. A radiance, a light in their eyes. When they laugh or smile, they dont care how pretty they look.
They do it because they want to.
For males, its pretty much the same thing, though i prefer someone that is decently animated. Eyes are the hugest thing ever for me. to see a depth of intelligence in their looks, that sort of thing.
Also, on a semi related note. When people tend to fake smile. their eyes are generally open and do not change. Like model smiling 90% of the time. A real smile, it doesnt matter if they show a bit of gumline, if the skin around their eyes crinkles a bit. They are merely smiling.
That realness is completely sexy to me.