I'm generally with the guys who have said "a gift is a gift", so there is nothing you can or should do now. I guess my only question would be how "close" you are to the groom. If this guy was one of my two or three closest friends, I'd be really hurt by his decision to re-gift. In that case, I don't think I could keep quiet forever. It might take a year or more, but I'd do something to let him know that I knew of the re-gifting. If, on the other hand, this was not a very close friend, I'd let it slide.
Are you certain this was a re-gift? Is it possible that he was so impressed by your gift that he went out and purchased the same thing for his friend?
If not for the Seinfeld episode, this probably wouldn't be an issue for any of us.