Google just announced Google Custom Search Engine, which allows you to create your own custom search engine and stick it on your site with a few lines of code. I was able to add one to http://www.developmentnow.com is about 5 minutes (look at the bottom of the blog page, or in the groups section e.g. at the bottom of this thread about web services).

One downside is that it relies on Google’s index, so if your site isn’t well indexed by Google (which mine isn’t) your results are limited. But, it would be a nice thing for budding webmasters who don’t want to build or maintain their own search engine, especially if they made sure to populate Google’s index with Google sitemaps. And of course they make it really easy to incorporate AdSense into the search results.