Google custom search Engine can be a great money making tool along with your Google adsense.
Google has released tips for setting up a search box on your Web site.
1. Make your search box easy to find.
2. Make sure your search box is always available.
3. Customize the appearance of search to fit your site.
4. Experiment.
5. Be open to feedback. Ask for it.
6. Learn what users are looking for.
7. Let visitors know who powers your search.


If you don’t have a search box you can consider using the Google Custom Search Engine, which is available in both free and paid versions.