The person who originally posted indicated a desire for a bus powered external hard disk. At work, my company provided me with this one, the "firelite,"
http://www.smartdisk.com/eWeb/smartd...iteporthdd.asp
... it is 3 years old now and still working fine. The one they gave me has 80 Gig, and I've used in exclusively to make clones/backups. It is a firewire bus powered disk, so there's nothing to plug in except the firewire cable to your macintosh.
[An aside -- I think this "firelite" disk comes with a simple version of "bounce back" which is probably something of a competitor to SuperDuper. I must say that I was never tempted to try something different from SuperDuper because SuperDuper works so well. And I don't even use half of the capabilities of SuperDuper, all I do is manually perform clones and then manually do Smart Update once per day. However the "firelite" disk itself works quite well for cloning purposes.]