I have written about the site: command in Google before.
The site: command in Google is an invaluable tool for doing Investigative Internet Research (IIR), especially in combination with other advanced operators.
Google site: Tool
Google site: Tool only works Firefox 14 or later on Windows 7.
It allows you to add site: or -site: to modify your Google search results. To limit your query to a particular site in the results, or to re-run the query excluding that site from the results, click the green URL below the result header. This works best on Google.com rather than the country-specific versions of Google. It also works on the encrypted version of Google.com.
This addon requires Greasemonkey.