Confidence. I do tend to strut a little, walk with my head high and my heels on (although 9 times out of 10 this rules out most men under 6'3, tall freak prior to heels, y'see!) and I notice more guys pay me attention than my more shy and retiring type friends.
If you know you look good, it's pretty obvious and I think guys find self assured girls attractive. Well it never did me any harm.