It turns out Amazon does have a shopping cart for other eCommerce sites. It is similar to Google Checkout. One advantage of Amazon payment is that many people already have an amazon account, so they don’t have to sign up new accounts. They can use their existing Amazon account to make purchases. The bad news is that Amazon payment is relatively new compare to Paypal and Googlecheckout. I haven’t found a sigle popular Worldpress ecommerce plugin to support Amazon payment. If I want to use Amazon payment, I need to write more custom pages than using a plugin.