Filezilla is a great, open source, FTP client that I have been using for some time now.  If you're undecided on an FTP client give it a try and download Filezilla.  When using Filezilla for the first time I recommend tweaking the file transfer settings.  Recently I had a couple co-workers new to Filezilla mention to me that file transfers were slow and taking a long time.  After taking a look I realized the default Filezilla file transfer settings were the culprit.

By default Filezilla is configured to support only one simultaneous file transfer.  On anything except the slowest connection this is going to be unneccesarily slow when transfering multiple files, particularly when those are small files that are not saturating your connection.  To adjust this setting, go to the Filezilla menu bar and select:

and set "Maximum simultaneous transfers" to something higher than one.  I work on a very fast network and always set this to the maximum value of ten.

So, if you're using Filezilla nad can't figure out why transfers are taking so long or why you can only transfer one file at a time, there's a good chance that you're only configured to transfer one file at a time.