Google APIs: Search, Advertising and Commerce
Google offers APIs in the areas of Search and Advertising, exposing them using various technologies: SOAP, REST and Ajax. The Google AJAX Search API lets you integrate a dynamic Google search module into your web pages so your users can mash up Google search results with other content on your site or add search results clippings to their own content.
The Google Data Calendar API is the first of the new REST Google Data API that lets you search and manipulate Time based information.
The Google AdWords API allows you to automate ads creation and management on Google AdWords.
The Google Checkout API helps you integrate Google Checkout in you ecommerce infrastructure.