Have you looked at Atomz Search? It works really well. If you use their freebie version you have to include their logo on your search page (and a 500 page limit) but considering the high end quality of their indexing service I think it's a fair trade off.
www.atomz.com/search
Regards,
E3
Atomz Search is the award-winning site search solution delivering fast, meaningful results to hundreds of enterprise Web sites.
Atomz Search fits seamlessly into any Web site and gives fast and accurate search results with complete control over relevancy and search result attributes. Atomz offers a free, unlimited trial (Atomz Express Search) that users can easily implement on their Web site. The trial version is feature-limited and has a 500-page limit. The trial version of Atomz Search
is ideal for personal and small business Web sites.
BTW, I don't know if you can run ASP but this is a real good one:
http://www.esolutions.com.au/articles/Yider.asp