http://code.google.com/apis/ajaxsearch/ Google is your friend because they supply the code and the method of finding it
The Google AJAX Search API lets you put Google Search in your web pages with JavaScript. You can embed a simple, dynamic search box and display search results in your own web pages or use the results in innovative, programmatic ways. See the examples below for inspiration.
The Google AJAX API's are useful for more than just Search. Now they even host the latest stable releases of some popular javascript libraries like jQuery and Prototype. Now you don't have to host those libraries on your server, you can just load them from Google's servers.