Every man should own a good pair of sunglasses. They aren't just for style, either -- they protect your eyes from harmful UV rays. But yes -- they also make you look dashing. In recent years, aviators have become a popular sunglass choice among men (as you can see by Brad Pitt's example).
Style aficionados recommend you wear your aviators (or other stylish shades) with formal dress and purchase another cheap, sporty pair for golf, hiking, biking -- and whatever other outdoor activities you enjoy. No need to spend a fortune on the sporty pair -- that way if they get lost or broken, it's no big deal. And never wear your sports sunglasses with business attire. Fashion faux pas!