I fully agree with Bozola. The terminal FTP is sufficient for much of my FTP needs. However, I don't know if it supports SFTP (which a number of services require). Otherwise, while not "freeware", Fetch is a longstanding Mac FTP client... and can be used even after the trial period expires (just be patient).
-edit-
Ahh, I see terminal has sftp as well. Excellent!