Sharepoint - SharePoint Search: Exclude lists and listitems from search results

You want to create Search Scopes. You can create them globally though the Shared Service Provider configuration or at the Site Collection level through Site Settings.

Check out: Creating and Exposing Search Scopes in SharePoint Server 2007 Enterprise Search

Create search scopes using ContentType and ContentClass to limit the results to what you desire.

example

Be warned that for search scopes using ContentType, pages that are set to be the "Welcome Page" for the site lose their content type for the search index and are classed as having a content class of a web site.

You can also exclude a specific list using the setting List Settings -> List Advanced Settings -> Allow items from this list to appear in search results