When the wedding invitation calls for formal or black-tie optional attire, men have it easy. They can wear either a tuxedo or a dark suit and tie. But what should women wear? A formal cocktail dress is totally appropriate, but an evening gown is so much more fun. (How many times do you get the opportunity to get really dressy?) Add glamorous makeup and dramatic hair and jewels and you're all set. Here's some inspiration for deciding between a cocktail dress and an evening gown.