Although it is less common these days for men to style their long hair, a braid can look uniquely elegant when he wants to dress up, or be simple and utilitarian for just keeping his hair out of his face.
Most men I've met tend to feel a basic braid is the most masculine look for them, either with a full braid or a half braid. Still, many are happy to experiment with a classic style or go all-out and original with a letter braid. The Legolas style is a popular one, which uses a herringbone half braid and two small french braids on the sides.
For more pictures of braids I've done on men, see my Flickr set here.