All Search Engines
The databases used by search engines are made by "robots" or "spiders" that automatically map the Web by following the links between sites. The directories, on the other hand, contain sites that are hand picked by human beings. Still, most search sites present search engine as well as directory results. Metasearch engines gather results from several search engines and directories. They are not that good at advanced Boolean searching, but may provide you with a broad sweep of the Web.
Traditional search engines list normal webpages and some other file types that are interlinked to from such webpages. The database sites, however, give you access to data that are not part of the Web as such. See also sites focusing on the hidden Web below.
Search Engines
Local Search
Meta Search