Working with online files, whether this is as part of running a website or just making use of online storage, an FTP client is virtually essential. Transmit is a feature-packed FTP client for the Mac which offers support for FTP, SFTP, TLS/SSL, Amazon S3 and many other cloud services.
The column view means that working with remote files is similar to working with those stored on your hard drive and you have the option of editing remote files using the applications you would normally use. Uploading files can be achieved by simply dragging files to the dock and you can use the program to keep multiple Macs synchronized with each other - and transfer status is always visible
Your most frequently used servers can be bookmarked and the tabbed interface means that multiple connections can be managed with ease. Support for Automator actions means that common tasks can be automated.
This is a hugely versatile tool that helps to blur the distinction between remote and local files. There is also a free transmit widget available that can be used to add access to the program to the dashboard. This can be downloaded from here.
Decent OS X FTP clients are a little thin on the ground, but Transmit is a great piece of software.