Our API directory now includes 112 advertising APIs. The newest is the TagLabs ActiveTag API. The most popular, in terms of mashups, is the Google AdSense API. We list 74 Google AdSense mashups. Below you'll find some more stats from the directory, including the entire list of advertising APIs.
In response to developer feedback, Twitter will soon add semantic versioning to its Ads API so that developers can more easily deal with new and deprecated features. Additionally, Twitter is increasing the time it supports deprecated versions of the Ads API from 30 to 90 days.