Google has created Google AJAX Search API, a JavaScript library that allows you to embed many flavors of Google Search into your site: Web Search, Local Search, Video and Blog Search. You can combine the search results from all these sources to obtain a beautiful sidebar like this. What's really nice is that you can customize the search box, the sources and the search is triggered on page load. Users of the site can use the search results to paste them in comments or other user-generated content.
Google AJAX Search API supports Firefox, Safari, and IE 6, it's still in an early phase of development and it's likely that it will include ads in the final release. This is probably the best API ever released by Google and it will certainly be more succesful than Google Maps mashups.
So it seems that Google tries hard to open its content to sites - they launched many APIs lately: GData, AdSense API, and now this very powerful Search API.
{Thank you, Garrett French }