dmoz.org

If you only ever submit your website to one other directory, the place to be listed at is the Open Directory Project (http://www.dmoz.org).

The Open Directory Project is the largest most comprehensive human-edited directory of the Web, and most importantly the data in this directory is used to populate many of the worlds leading search engines. Having your website featured in the Open Directory Project will therefore greatly increase the chances of it also becoming listed in many of the largest search engines.