The front squat is essential for leg strength and maintaining a correct back position for pulling. This was Eddy Copplin’s favorite exercise for deadlifting, having pulled 826 at 186 body weight. It builds the spinal erectors as well as the legs. (We use a front squat harness.)

http://www.westside-barbell.com/Articles%20Top%20Ten/Articles%202007/07Nov_the_squat.pdf