Seated cable row (aka pulley row) is a great back exercise. It's easy to break form here, so be sure to keep your head up and your back straight. Try to keep the weight on your back muscles at all times (do not pull with your arms). As you bring the weight back try to pull your shoulder blades together and flex your lats. Don't go back to far - go to a 90 degree angle, then lean forward, pivoting at the hips. Think of your arms as hooks to hold the weight. Make your back do the work.