I don't know of any FREE ones, but eOffice has the ability to send faxes (no charge for sending faxes, but you have to purchase the eOffice software).
I used to use Communicate! Deluxe on my PC. It was configured to e-mail received faxes to me, plus had the ability to poll an email address for sending. You have to have an available phone line and purchase the software to use it.
There are a lot of services out there for sending faxes (such as myfac.com). Most have about a $10/mo charge, but give you your own fax number for receiving faxes.
I would love it if Google Voice added a fax receiving option. Then that could be paired up with eOffice and sending/receiving would all be covered.
Popfax.com provides a low monthly fee for fax service that helps you or your business eliminate the costs of a fax machine, long-distance service, additional phone line, and it reduces paper costs as well. Also new features are available: registered fax, popcompanion, fax mail merge and many others.
