ThredUp.com: If your kids outgrow their clothing 20 minutes after you cut the tags off, you may love this site. Simply order a prepaid shipping bag, fill it with gently used clean clothes, and send it in to earn cash or credit toward the next size up.
TradeAway.com: Through this site you may either barter or sell for cash. You must assign your item or service a monetary value.
U-Exchange.com: Besides items and services, this international site has listings for vacations, home exchanges, vehicles, boats, and more. Search listings by location.
A final reminder: Bartering can be a great way to save a few bucks, but keep your eyes open.