I recently implementd the free version of Site Level (
siteLevel - Internal Site Search) on one of my websites.
The search executes on their server, so there is no code to install on your web server.
The results page is fairly easy to customize, and you can re-jig the search box code they give you to fit just about anywhere you like.
In addition, it provides what it calls "slices", which allows you to create a search box that searches user-defined sub-categories of your website.
It also provides reports, but I haven't had a chance to determine their value yet, since I just got started with it.
...Duane