Google Custom Search allows you to create a custom search engine for your site. The problem is the advertising is sometimes too intrusive, even when no results are found.
If that bothers you, then you could use the regular Google search with the sitesearch flag turned on.
<form action="http://www.google.com/search" method="get"> <input type="text" name="q"> <input type="hidden" name="sitesearch" value="labnol.org"> </form>
This is how Wikipedia offers Google search as an option. Of course, Google Custom Search has other perks like Adsense integration, look and feel modification, and search refinements which you would miss out on.