The search function included with the oscommerce shop is very limited since it doesn't search the products descriptions. This contribution not only adds that option to the search, but it also adds the ability to search attributes and files and to control those searches by limiting the search by price and category - a complete site search. If nothing is found in the search, it offers the customer a form where they can email you about what it is they are looking for. This is important since a customer may assume you don't carry what they are searching for if it doesn't show up in the search results.
We use it here. Give it a try to see how it works.