Jungledisk is great. Its easy to use, cheap and runs on Windows, Linux (includes GUI and CLI) and Mac. You can treat is as a network drive or setup automated backups. The protocol is open so you can use tools like S3 Firefox Organizer to retrieve your data outside of the Jungledisk front-end.
Another big plus is that you can run an unlimited number of instances across any number of machines after paying a one time fee of $25.