There are lots of great FTP clients out there for Mac OS X, but my favorite is Cyberduck (if only because the icon is so darned cute). Recently Cyberduck 3.0 was released, and it brings with it a bunch of neat new features, including:
- Support for WebDAV
- Support for Amazon S3 (that's Amazon storage cloud service)
- Bookmark searching
- Quick Look for files in the Cyberduck browser (this is pretty cool)
Cyberduck is free, but donations are encouraged.
Update: The previous picture was of version 2.x. Sorry about that!