I've just found another free FTP Client which is much better than any of the others. It's a lot more polished and contains many similar features to Smartftp.

It is called WinSCP http://winscp.net/

It doesn't have tabbed sessions, but it can open more than one ftp connection at a time and you can jump between then from either a pull down box, or shortcut keys.

It has a download queue, but I've not tried it out yet.

It has directory tree navigation (the first I've found).

It is also very fast and easy to use.

It also has direct SSH support with integration with Putty which is great for me, and it can uncompress and compress files remotely which is very useful and saves having to type SSH commands to do it.

It is however missing a few of the advanced features that are nice in SmartFTP. There is no advanced download queue, no download speed graphs (that I've yet to find), and the ftp transfer log activity is displayed in a separate window instead of being docked to the bottom of the main client's window. But other than that it is good and the FTP Client I will be using for the moment.