Our API directory now includes 56 billing APIs. The newest is the Merchee API. The most popular, in terms of mashups, is the Stripe API. We list 5 Stripe mashups. Below you'll find some more stats from the directory, including the entire list of billing APIs.
X.commerce is the new brand for the developer commerce tools that include the eBay API and PayPal API. The first conference under this new brand is coming in October to San Francisco. As a media partner, we have a promo code, as well as a little more information about how the company is looking to create a sum greater than its parts with the X.commerce platform.