Our API directory now includes 134 security APIs. The newest is the Universign API. The most popular, in terms of mashups, is the Google OpenID API. We list 8 Google OpenID mashups. Below you'll find some more stats from the directory, including the entire list of security APIs.
It's clear by the running total on the ProgrammableWeb homepage that there are a lot of APIs. In addition to a lot of companies with APIs, there are companies with a lot of APIs. Google has the most--surprised? You may be at some others than make the list, from social networks to online marketplaces.