Update: Google has apparently discontinued Site Search in favor of "Custom Search Engine". As there is already another Drupal module that implements that, I am deprecating this module in favor of the Google Custom Search Engine module. There will be no 6.x port of this module.
Google Search is a very small module that provides a search block that uses Google's Site Search functionality to search the current site. It is an alternative to Drupal's built-in search functionality. Pairing this module with XML SiteMap is probably a good idea.
Please be aware of the Google Site Search Terms of Service before using this module.