We use the powerful and flexible Phantom Search Engine. We have the ability to search your site AND any other sites that may be related (it's a good idea to get permission first!).
You can also allow users to set "agents", which will notify them by email when there are new or changed documents relating to their initial search.
Users can specify keyword searches, "begins with" searches, and/or phonetic searches; They can also search for changes in the past week, the past month, or contained in the last update. On top of that, they can include searches of URLs, headers, and page titles.
See the search engine in action
Please contact us to discuss your search engine needs, so that we can tailor a solution that best fits you.