A friend of mine chose a birdcage veil to accent her halter down. Because the gown does not have many sequens or accents on it, she is able to use this small piece to show a little vintage glamour, matching her theme. Had the dress been covered in sequens broken up with lots of lines, I would have suggested her to go with a more plain headpiece. Another bride chose beautiful chandalier earrings, and a thick, rhinestoned bracelet. After seeing herself in the mirror with the whole ensemble, she wasn't overly happy with the bracelet. I then gave her a smaller tennis bracelet with small rhinestones that were the same size of the rhinestones on her dress. She decided to go with the latter.
If you can't find what you are looking for, you can always have something custom made to match your gown. There are various boutiques that will put together barrets, veils, combs, pins, etc. It may cost you a little more than David's bridal, but at least you can say you designed it :). Clarissa's Boutique in Pittsburgh Pa is just one of these wonderful stores. http://www.clarissaboutique.com/html/veils.html
Ladies, just keep in mind that the simpler the dress, the bolder the accessories, and vice versa. Good luck!