Zoom Search Engine software
Free Find -
Google Site Search -
Web Assist DW Tools for Google (free)
there really are a great number of possibilities, as said above. Some of them you could find by using the search function here in this forum.
And this a German website although, but very easy, effective and easily to adapt:
A small note in the end: Using the search function of your website, visitors will be able to find every page or information you loaded to your server. Maybe this is not always desirable (website under construction or something like that).