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.
The travel site Orbitz has partnered with Google to show a virtual walking tour of the neighborhood around a hotel. You and I know it as the Street View API, part of Google Maps (our Google Maps API profile).