this is what I used: http://dcfldd.sourceforge.net/
the command i used was the following:
"dcfldd if=/dev/sda of=/dev/sdb bs=32M" without the quotes
"if" is the source, "of" is the destination, "bs" is the block size. for usb 2.0 connections, a block size of 32M seems optimal, if they're both sata, you can possible try 64M or 128M size blocks