rdiff-backup is awesome. It's a POSIX backup tool providing a (possibly remote) mirror and an incremental difference history (should that be decremental history?) of the mirror.
BackupNinja (website currently down) is even better. It's a curses (ie text based) wizard for setting up a number of backup tools including rdiff-backup and mysqldump. It does all the fiddly bits like handling ssh keys and setting up cron jobs.