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:
Mac Imaging Software: clone a master disk image to a computer's hard disk while that disk image is hosted locally, on a network via AFP, NFS or multicast, or on the internet via HTTP.
rdiff-backup backs up one directory to another, possibly over a network. The target directory ends up a copy of the source directory, but extra reverse diffs are stored in a special subdirectory of that target directory, so you can still recover files los
DiskWarrior is the most highly decorated Mac disk repair utility ever. It repairs disks that no other program can repair. New hardware monitoring helps protect your data from drive malfunctions.