CarbonCopyCloner or SuperDuper.
CCC is free to download and use for 30 days (hint: if you download the completely free version 3.4.7, it will work too, but you will have to dismiss the alerts that it "hasn't been tested with the latest Mac OS").
I haven't used SD in a while, but it used to be completely free if all you wanted to do was create a "full" clone (i.e., not an "incremental backup").