I personally use CuteFTP Pro.
Simple interface, lots of neat options, but it's payware. There is a non-pro shareware version that's also neat, but doesn't have all of the bells and whistles of the Pro version. However, it has more features than many other FTP clients.
I've also used several others that I'd recommend.
SmartFTP is a nice simple FTP client that has a ton of features for a freeware app.
BulletProof FTP is very popular, has a fairly simple interface, but is very feature-rich.
I've also used Hummingbird FTP, which basically makes the FTP session look like Windows Explorer, which means it's simple for drag and drop, and the like. However, it was part of an expensive suite of networking tools, and I don't know if it's cheap or even available by itself. Given the choice, I'd go for one of the others anyway. I don't care for the "Explorer"-like interface, but that's purely personal preference.
I would not recommend WS_FTP. I don't care for the interface, and while the LE version is free, it's extremely feature-limited. In terms of freeware, you'd be better off with SmartFTP.
You'd probably be much better off with any of the others, but it comes down to registering the one you're most comfortable with.