For American Express cardholders, ShopRunner continues to offer a ShopRunner Perpetual Membership for free when you enroll with your American Express card and keep it as your default payment method. (Your membership may be canceled if you remove the American Express card as the default payment method.) That's tied with our mention from last month as the best offer we've seen for this shipping service. It includes unlimited free 2-day shipping, free shipping on returns, and more. Some of the vendors that use this service include Toys "R" Us, Lord & Taylor, Calvin Klein, eBags, and drugstore.com.