While cleaning out the closets, or looking for clothes for your new size, consider Buffalo Exchange. You can trade in your old, clean clothes for a store credit or cash. One friend who recently lost 80 pounds kept recycling three pairs of jeans. As she lost a size, she took back three pairs and picked up three pairs in her new size.
It's also a great way to clean out the closet.
Also check out Play It Again for buying and selling used sports equipment.