SuperDuper!

I'm a big fan of SuperDuper!, the free backup and disk copying utility that specializes in creating bootable backups:

We do this by quickly and efficiently creating a fully bootable copy of your source drive. Perhaps more importantly, recovery is near immediate, even if the original drive is completely unusable, because you can start up from your backup and continue working.

I use it if I'm going to vaporize the contents of the boot volume (to prepare for a clean install of Mac OS X, for example) to ensure I can roll back to the original set up. You can also use it to maintain a bootable backup using the Disk Image Read/Write "Sparse" Bundle option, which I also like to use to back up before I erase.

To make SuperDuper! part of your daily backup routine, you can purchase the full version,

to unlock scheduling, Smart Update (which saves a lot of time), Sandboxes, scripting and more.

Worth $27.95, I think.