tpc.int - The only continuously, completely-free internet fax service on the web.
Internet Fax FAQ - Answers the question "How can I send a fax from the internet?".
eFax - The world's most popular internet fax service with millions of users.
Internet Fax section in the Open Directory (DMOZ).
Fax from Microsoft Office - Internet Fax services which support integrated faxing from within the MS Office suite.
List of personal internet fax services on slipstick.com.