I'm a big fan of SuperDuper! myself, but Carbon Copy Cloner has also long been a great, low cost option for cloning hard disks in OS X (indeed it's been around longer). Mike Bombich has now released version 3.1 of CCC implementing rsync 3.0.0 "to provide even greater fidelity when backing up using the 'Copy selected items' backup method." Other improvements includes an updated interface and various bugfixes, etc.
Carbon Copy Cloner is a free download from Bombich Software (donation requested).