zoom search works very well. Especially with php. Very easy to use and has a great GUI interface. Its basically an indexing software. It even builds all your php code for you and even your search form!
Google works well enough, but some site owners dont like that fact that google search takes their visitors away from their site briefly. I have heard that google now has a custom search that doesnt do this, but havent check this myself.
Just remember though, Zoom is free and fully functional, but they limit the free version to 50 pages to index I think. They have paid versions which allow for more pages as well as unlimited number of pages should you need that in the future.