freeFAX.com: freeFAX.com has been funded by ad revenue, not user fees, since August 2000.
faxZERO.com: This is a truly free online faxing service that makes its money by placing ads on fax cover pages. Pay $1.99 per fax to remove the ad.
K7.net: Free faxes and free voicemails are delivered directly to your email inbox with K7’s unified messaging service. K7 does not offer an out-going fax service.