The Google AJAX Search API is “an experimental API that 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 AJAX Search API is currently in Version 0.1 and its an experiment designed to get developer feedback. Version 1.0 to be launched later will likely contain advertising. To use the API, you must sign up for a Google AJAX Search API key, which you’ll include in the URL with which you access the API.
The AJAX Search API is available for all sites that are accessible to consumers without charge. The Google AJAX Search API is currently available on Firefox, Safari, and IE 6. Put Google AJAX Search on your web site.