The newest addition to Gmail Labs is an option that adds a Google search box to your Gmail inbox interface. When activated, the search box appears below the “Labels” section of the left navbar, like this:
(Of course, there’s a drag and drop option in Gmail Labs, too, that will let you move the search box wherever you want in the left navbar.)
When doing a search, the results appear in a new window that overlays the bottom of the email list. From my testing, you’ll get a max of three search results and no more than one AdWords ad. Clicking one of the search results will open the page in a new window or tab. The search box also includes options such as “Send by email,” “Reply with result” and more, depending on what you’re doing in Gmail at that moment.
The Google search box can be activated by going to the Labs tab under Settings. You can read Google’s announcement for more details about how it works.