Big arms are one thing. Having a wide back can really round out your upper body development. When your shoulders and back look wider, the waist looks smaller by comparison, helping to create a V-taper. In general, pulldown and chinning exercises are the best movements for back building. Here are my favorite choices for developing wider lats:
Wide-Grip Chins - This is the premier exercise for building a wider back. It's more difficult to perform than the lat pulldown exercise because chins requires a good deal of strength to pull your body up for reps. However, once you master the form, you'll be well on your way to hugeness.
Grab the bar slightly wider than shoulder width. Arch your lower back and tilt your head toward the ceiling. Pull your body up, trying to touch the upper section of your chest to the bar. Keep your elbows pulled back at the top of the movement.
Wide-Grip Pulldowns - This is probably the most popular exercise for widening out those lats. It's similar to wide-grip chins, except for the very convenient fact that the weight can be adjusted to your strength level. So if you aren't strong enough to do chins, wide-grip pulldowns make a very good substitute.
Position your legs under the bar and employ a grip that spaces your hands reasonably far apart. Arch your lower back and stick your chest out before initiating the movement. Slowly pull the bar down to the upper section of your chest, keeping lower back arched and elbows pulled back. Return to the top for a full stretch in the lats before starting another rep.
Pulldowns Behind the Head - A variation of wide-grip pulldowns this exercise has a reputation for potentially straining rotator cuff muscles. By practicing the movement with a slight variation you can more safely develop upper back muscularity.
Sit backwards on the lat pulldown machine facing away from the weight stack. Take a slightly wider than shoulder width grip on the bar and pull down until your upper arms are parallel to the floor. Squeeze your upper back muscles at the finished position, feeling the upper back and lats contract. Start out using a light resistance and work your way up to a moderate load. Play it safe and avoid going heavy with this exercise.
Natural Mr. Olympia