Faxzero is a free service that is advertiser supported by putting an advertisement on a coversheet that the recipient sees. You cannot receive faxes with this service, but you can send up to two free three page faxes a day. For longer or advertisement free faxes, there is a charge of $1.99 a page via Paypal. Faxzero supports .doc or .pdf files or a text based message. You cannot receive faxes using this service.
The eFaxFree plan allows you to get a fax number (not always a local number) that sends faxes as an attachment in your email. You can receive up to 20 pages a month free with this service. You cannot send faxes for free using this service, but do have the option of paying for a monthly fax plan with many other features.
Drop.io is an online file service that serves as a virtual drop box for your files. You can receive faxes as .pdf files to your drop. With a premium account (starting at $10 a year), you can send .doc and .pdf files to a fax number.
These services are monthly subscription plans that allow users to send and receive faxes. Most of theses services give you a local or toll free fax number and allow you to manage faxes online without requiring a fax machine. Pricing, number of included pages, and other features vary by provider and plan. Please check out these services individually to see what best suits your needs.