"A search directory is similar to a search engine in that they each compile databases of web sites.
A directory differs in that it only enters sites that are directly submitted to it and instead of crawling a site they send humans to inspect and decide if your site is worthy of a listing.
The listings are then categorized and normally alphabetized so that the results of any search will start with site descriptions that begin with some number or non-letter character then A to Z."
Yahoo directory Yahoo ! offers an excellent Directory service; above you can see many of the categories in the Yahoo ! Directory.
Yahoo! provides both a search engine and a directory service, and the directory is searchable separately from the rest of their search engine results.
You can also subscribe for RSS updates when new additions are made to directories.
Other major Directories
Hot Vs. Not: Web Directory
Resource Discovery Network
Student Navigator (a comprehensive set of academic resources)