If Time machine is single most important feature for OSX (in my opinion), then Super Duper is the other program for backup. And it has just one feature that matters to me.
Bootable backups.
Simple
I have an external drive (USB because it’s cheap and the speed doesn’t matter so much). Plus it on, tell SuperDuper to use it for a backup.

Then the backup will happen and you will have an image of your HDD. Note that SuperDuper has a SmartUpdate so once the original back is done, it will just update the incremental differences and make the backup shorted.

But the best feature is the one that happens after the Successful Copy. The external disk drive is made bootable.
If I really had to, I can plug it into ANY MAC that supports the OS (( I’m running Snow Leopard so it has to be an Intel processor system )) , power that MAC on, press the C key at startup and select the External USB drive to boot from.
It will be slow, and might take a while. But, YOU CAN BOOT FROM YOUR BACKUP without having to restore. That’s smashing.
Shirt Pocket
You can buy SuperDuper from Shirt Pocket and it costs USD$27.95/GBP£19.98.
Greg,
Another great Mac app for creating bootable backups is Mike Bombich’s Carbon Copy Cloner.
Also the basic version of SuperDuper is free. If you want scheduled backups you’ll need to pay.
Both are very handy for transferring data before a disk upgrade.
Robin