Interarchy File Transfer for the Macintosh
I’m definitely not up to date on happenings in the Mac world (the last one that I used had a main memory size measured in kilobytes), but this application looks really good nonetheless. It supports a wide variety of protocols and storage systems including several varieties of FTP, SFTP (SSH File Transfer Protocol), WebDAV and of course, S3.
The fact that you can automatically mirror file system changes (local to remote and vice versa) makes this a great tool for incremental backup and for keeping multiple machines in sync with each other. The user interface is available in English, French, Japanese and German.
There’s a free download, with a full license available for a reasonable price.