Duplicity performs incremental, encrypted backups onto a range of interfaces including scp, ftp, rsync, WebDAV and Amazon S3. It uses standard tar, rsync and GPG tools, so the data can be recovered manually.
Article explaining how to mount an encrypted container on a remote system. The remote file container is mounted over sshfs then locally mounted via dm-crypt. This has some major challenges, the approach is interesting albeit not particularly practical.
Encrypted backups which don't require you to trust the backup provider, although the code is open source but not free (as in freedom) and so there is only one possible provider...