Darin Slack's F4 Quarterback development series are the best in the industry and there is no rival when it comes to presenting material for easy absorbtion.
If you've received the mind-blowing C4 series and have the fundamental knowledge of throwing biomechanics and self-correcting, be sure to enjoy the F4 series that covers a wide array of fundamental-enforcing drills and competitive challenges. This series progresses your quarterback through living and operating like a quarterback though footwork, upper body, trunk, and mental training.
Of particular interest, was the final DVD of the series that established easy-to-use training methods that cemented proper alignment and mechanics of a thrower. This is a great tool for reinforcing the elements of C4 as well as slowing down the throwing movement to waypoints to enforce disciplined biomechanically correct throwing motion.