Fugu gives an interface to the commandline Secure File Transfer (SFTP). The whole application is encrypted letting you upload and download files in total security.
Fugu offers an interface that, if not a little rudimentary, is similar to most FTP clients. You can browse through your directories, drag and drop files and preview images. Fugu includes full directory upload and history.
In terms of security, not only does Fugu handle SFTP, but you'll also find it works with SCP and SSH. You can create your own SSH tunnels, perfect for transmitting encrypted information. Fugu also interacts well with your Mac's Keychain and handles Public Key Authentication.
Fugu works with external editor and you securely change your permissions and owner or group access. The application can also connect to alternate ports.
The interface may not be that sexy, but Fugu is a very reliable SFTP client. What's more it's completely free!