This is a very worthy organization as well as a place to find dresses marked WAY down.
The Brides Project in Ann Arbor takes donated dresses from brides and resells them (yes they are cleaned) at a significant discount. They are having a sale THIS Saturday, first come first served, from 9:30 am to 12:30 pm. They give their profits to the local Cancer Society. Go to their page and read some of the stories, they are really inspiring.