In Chicago today eBay will kick-off of their annual eBay Developer's Conference by announcing Project Echo, a way for outside developers to integrate their apps "directly onto the world's largest ecommerce site".
It's not often we see an API "go on sale". But that's what Google is doing with their announced a Google AdWords API. They have a new version update but along with it, they have "holiday season API sale pricing". The details of the holiday sale are spelled out in the October 20 AdWords API blog post "Happy Holidays! Enjoy more API units":