The following links will take you to email-based discussion list directories. This site has both a search engine and a browsable list for scholarly and professional discussion lists.
Lists Provides a search engine for general interest discussion lists.
This is a searchable site with nearly 100,000 lists indexed. The site is also browsable by subject. Yahoo's E-Mail Lists Yahoo provides a search engine for discussion lists as well as links to other list sites. There is also a link to the universal unsubscribe service. The following are maito links for several academic email-based discussion lists.