Restricted Search

While this module works well on small sites, it is not as robust as Search Restrict. There won't be a Drupal 6 (or 7) release for this module, so please use Search Restrict instead.

There is also the Search configuration module that for Drupal 7 now incorporates this functionality.

Restricted Search is a module which lets administrators exclude individual nodes or entire content types from the search system. This is especially useful for pages used with Login Destination, or CCK nodes primarily meant to be presented only with views and not as individual nodes.