Shirt Pocket just released SuperDuper! 2.0. SuperDuper! is a great backup and recovery application, but it's also a great system cloner quite useful to developers and testers.
You can schedule backups, of course, but most importantly to my eyes, you can make a clone of your system partition in minutes, allowing you to test software with no risk of affecting your main system and user data. And you can also save a copy of that brand new clone to a disk image for quick restoration. So you could have three disk image, one for Jaguar, one for Panther and one for Tiger, and you could restore any of them in less than 10 minutes into a working system, ready to test your application.
SuperDuper! really deserves its name. Congrats to Bruce and Dave!