Internet Fax Service: Limited free faxes and cheap premium account for ad-free faxes:
Fax Zero
I used it once in Feb. 2014. They returned a "successful" fax receipt. Their free service has ads on the cover page, but hopefully will not cause any problems. Keep an eye on it: this could be a very nice service, with the potential for very reasonable premium services! On their premium accounts, they have a nice choice: a low monthly rate, or a reasonable "per-fax" rate, payable through PayPal.