Instead of writing a PHP script from scratch, I wanted to know if there are any free scripts, plugins, or APIs out there that allow me to add a search box to my website to search only content on my site.
Google's free version is ad-supported, and I am looking for a clean, simple, and non ad-supported solution. Any ideas?
Check out the zend lucene extension. It provides a PHP interface to the open source Apache Lucene search engine.
Zend_Search_Lucene Documentation: http://framework.zend.com/manual/en/zend.search.lucene.html
Apache Lucene project: http://lucene.apache.org/java/docs/index.html
There are a number of these, one of them are sphider.
Here is a super easy way that works pretty well:
http://sitecomber.com/getsitecomber/
You can create code to paste into your site in about 2 minutes. It doesn't get easier than that. Search is powered by Google, but results are isolated to your website.