One of the questions I get asked most frequently is, "how do I big build big powerful shoulders?" I usually answer this question by listing the following two exercises. Firstly, the best all around shoulder building exercise is the barbell hang clean and press. You perform this exercise by bending over with a barbell in your hands and a shoulder width grip. Start with the barbell just above your knees and be sure to maintain perfect posture with your head in line with your spine, chest up and back arched. Initiate the movement by driving your hips forward and shrugging your shoulders. Pull the bar to your upper chest and catch it there by dipping at the knees slightly. Immediately press the bar straight up overhead to lockout.
Do one or two heavy set of 5-8 reps, rest 90-120 seconds and then, if you really want to fry your shoulders, do a backoff set with a lighter weight for 10-20 reps. This will smoke your shoulders and build them up better than just about anything else.
The other best shoulder exercise you can do if you want to build cannon ball sized delts is a handstand pushup. This is as difficult as it sounds but can be modified for novice or intermediate lifters. The easiest way to work up to a handstand pushup is to start by simply holding the position for time while you keep your feet up against the wall. Work to increase your time each week and eventually you will be able to start doing partial reps. Allow your feet to slide up and down the wall and aim to increase the range of motion each week. Eventually you will be strong enough to do a single full range rep, going down until the top of your head lightly touches the floor. From there you will work up to doing a set of 5-8 reps.
After you can do that you will need to add greater range to increase the difficulty of the exercise. To increase your range of motion place your hands on two boxes and lower your head down between them. Once you can do a set of 5-8 reps like that, with your head going all the way down between the boxes, you will have powerful shoulders that would make the Hulk turn the other way if he saw you coming. Do 2-3 sets once per week with 90-120 seconds rest on a different workout day than the one in which you do the hang clean and press.