After I got my dress, I found out about an organization called Brides Against Breast Cancer. They take donated dresses, sell them to other brides, and use the money to make the lives of BC victims a little happier.
http://bridesagainstbreastcancer.org/They often hold sales in various cities around the country, so, if you haven't found your dress yet, you might want to consider it.
I just sent it off and feel super good about it. I hope it makes the next bride as happy as it made me!