Resell good-quality designer clothing that you no longer wear at a local consignment store. These stores will sell your clothes and usually split the proceeds 50/50 with you. Sometimes you can either take cash for your clothes or earn more money in the form of store credit to shop for new duds. It's up to you.
Tip: Bring your clean, laundered clothes on individual hangers. And bring your out-of-season clothes (e.g. fall clothes in summer), because consignment stores sell clothes just like regular retail shops.