In the past I have used clients such as CuteFTP and WS_FTP, but these require payment of $30+, so my trials would always expire forcing me to change. Then, a couple of years ago, I came across FileZilla, one of the most highly downloaded applications from SourceForge.net. Not only is FileZilla open-source (under the GPL), but it is also available on all major systems - Linux, Mac, and Windows.