So, here's a new one to me: NewlyMaid. You mail in an old bridesmaid dress, and you receive credit (good for 18 months) toward a LBD (little black dress). The organization apparently only carries six styles of LBDs, but the site indicates that these styles are changed out intermittently. These are my top two current faves:
The old bridesmaid dresses that are turned in are either recycled or distributed to charitable organizations.
I haven't used this service, but I have a closet full of old bridesmaid dresses that I would love to pass on! And I have a wedding in October that just happens to require me to wear a LBD...hmmm...food for thought!