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Free Site Search Engines

PicosSearch
PicosSearch is easy to install, and offers fast accurate searching with no additional software required. This service is available FREE for popular default settings, or by business-quality subscription services with full layout control and advanced account management features.

FreeFind.com
I used this myself for this site and was happy with it. You can upload a template to customize the appearance of the results page and schedule indexing. Ads appear on the results page.

Atomz.com
I have heard good things about this service although I have not yet tried it. It will index up to 500 pages and there is no advertising - they require that their logo be at the top of the search results.

FusionBot.com
Give your web site its own search engine with no software to install. Offer customized site search, site map, and reporting services for your site in minutes.