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.
With the new version of OS X (Leopard) Apple has included some great functionality in Time Machine. Your Mac will automatically backup to an external drive every hour. It includes the ability to recover deleted files in a timeline.
Amazon's S3 is an online storage solution; you pay for only what you use ($0.15/GB/month, plus some transfer costs). I wrote a simple step-by-step guide to setting you a Mac to sync with Amazon S3; here's the executive summary version:
Flickr Backup is a Java application that allows you do download your photos and back them up to your harddrive or to media. This is useful if your local harddrive goes bad and you don't have a current backup.