We're using Cyberduck where I work for relatively light duty ftp work, and it does seem to get the job done for zero dollars.
Personally, I'm a longtime Interarchy (VERY longtime) for my heavy lifting at home. I like its interface, and that it can double-click a mirror file and have it scan a local folder containing nearly 3000 files and find only the differences that need to be uploaded in under three seconds, and I can even create special placeholder files in my local mirror so it won't touch specific stuff on the server that I want to stay there.
Worth the price to me (and I haven't even tried v9 yet), but it's probably overkill to most people.