Transmit is a fabulous FTP client for the Mac, which also does SFTP & WebDAV. I've always liked it, but the new version (3) has a couple of features which are really nice if you keep on your own machine copies of files which are on a remote machine:

• You can 'Link Folder Navigation' meaning that as you move through the tree of files on one machine, it automatically changes to the matching directory on the other.
• You can set up 'DockSend' for your favourites. If you drag a file from somewhere within your local filesystem onto the Transmit icon in the Dock, and it recognises the local origin as being within a directory that has a copy on the server, it will connect, upload the file to the appropriate place in the remote hierarchy, and disconnect again. Too cute.

It has loads of other features too, but these are the new ones that may not be known to existing Transmit users. Highly recommended.