Three kinds of tools to find resources on the Internet:

1.  Internet Directories (useful links, organized by subject)

SAILOR: Maryland public information gateway. 

Internet Public Library  

Librarians' Index to the Internet  

2.  Search Engines

Google

Yahoo

Alta Vista

Kartoo: Produces a map of results, rather than a list of web pages.   

Teoma: Suggests refinements to your search.

Vivisimo: Clusters results that are similar.

3. The Invisible Web

The Invisible Web: many databases are searchable but are not obvious in a list of retrieved sites via a search engine; this site shows how to search the Invisible Web.