FileZilla is a cross-platform FTP, FTPS, and SFTP client. It is fast, easy to use, easy to configure, and best of all, reliable. It runs on Windows (XP, 2000, and Vista), Linux, *BSD, and Mac OS X and is available in a variety of languages. A Windows-based server edition is also available.Downloading FileZilla is easy, requiring only a few simple clicks. Installing a new version over an older version will not alter existing settings, and a recent addition to the application allows for the choice between All Users and Owner during installation.
I can vouch for most of the above. I run it on seamlessly on Vista (which right away gives you an indication of FileZilla's reliability) and had no problems with the initial install and upgrades. I've tried two or three other FTP programs on a trial basis -- ones that you eventually have to pay for, mind you -- and FileZilla was easier to understand and get up and running than any of the others.
Adam writes that the latest version of FileZilla fixes some bugs that I never noticed and goes on to explain some more advanced features I've yet to explore, including a multiple-transfer function and this:
If multiple threads aren't enough, FileZilla will go you one better by allowing multiple instances. That is, more than one copy of Firezilla can be up and running at the same time. In practice this offers the possibility of uploading to multiple FTP servers or connecting to a single FTP server as more than one user.
FileZilla has a few minor quirks that Adam mentions, but his overall impression -- and my overall experience -- is that this freeware compares favorably to FTP clients for which many people pay up to $50.
If you want to check out FileZilla, you can download it from here.