Western Digital WD2500D032-000
Just as a point of interest I purchased the above drive (sold as MyBook). It's a 250GB external drive with USB 2.0 and Firewire 400 interfaces. I created 2 partitions, one of 80GB named Clone and the other taking up the rest named External 1. I have a PowerBook G4 with an 80GB internal drive running OS X 10.4.9 and SuperDuper 2.1.4.
I ran SuperDuper and cloned the internal drive to the Clone external partition through the Firewire interface. To test it I rebooted fron the Clone external partition flawlessly. I've since tested and retested booting from Clone without a single problem or error.
This drive also has a power adapter so it will not have the same problem as some other WD drives that rely on power from the PowerBook.
SuperDuper has become an invaluable tool for me and I have no urge to use any other backup application.