rsync hfsmode is a patch for rsync to enable recognition of Mac OS X HFS resource forks and Finder metadata, and to copy them to a remote filesystem. The destination system can be any OS and filesystem that supports rsync, so you can use rsync to archive Mac OS X files to servers running Linux, Solaris, et cetera.
Duplicity is a backup program that only backs up the files (and parts of files) that have been modified since the last backup. Built on FLOSS (rsync, GnuPG, tar, and rdiff), it allows efficient, locally encrypted, remote backups.
Based on this great blog post by Tim McCormack, I managed to write some scripts that back up files to Amazon S3. The files are encrypted with GnuPG and rsync-ed to S3 using a Python-based tool called duplicity.
C. Morbidoni, G. Tummarello, O. Erling, and R. Bachmann-Gmür. Proceedings of the 6th International Semantic Web Conference and 2nd Asian Semantic Web Conference (ISWC/ASWC2007), Busan, South Korea, volume 4825 of LNCS, page 533--546. Berlin, Heidelberg, Springer Verlag, (November 2007)