Directories

Archivum.info
Large archive of mailing lists and newsgroups.
http://archivum.info/

CataList
The official catalog of LISTSERV lists.
http://www.lsoft.com/lists/listref.html

Email Newsletters & Ezines at Tile.net
Large mailing list directory.
http://tile.net/lists/

I Want Newsletters
A large collection of free newsletters sorted by category.
http://www.iwantnewsletters.com/

listTool
A directory of lists that includes an easy way of subscribing and unsubscribing to them.
http://www.listtool.com/

openSubscriber
A mail-to-web gateway with searchable archives of public mailing lists.
http://www.opensubscriber.com/

Public Mailing Lists Managed by Arrow
A frequently-updated list of publicly accessible mailing lists managed by users of Roger Smith Software's Arrow Mailing List Server.
http://www.jadebox.com/arrow/list.html