"Directories are search engines powered by human beings. Human editors compile all the listings that directories have. Getting listed with the web's key directories is very important, because their listings are seen by many people. In addition, if you are listed with them, then crawler-based search engines are more likely to find your site and add it to their listings for free."
- Danny Sullivan
Being listed in some of the major directories like the Yahoo Directory and DMOZ (The Open Directory Project) can help your rankings in places like Google and Inktomi.
Search engines tend to give sites listed in directories a bit of a "boost" because in order to be listed in a directory, a real live human editor must review your site. The theory of the engines is that if a site has a directory listing than it must have some "redeeming" values, because it's "passed" an editors review.
We've found 3 great sites that list lots of good directories.
If your interested in quality relevant links drop me a line.