The "trapezius" (aka the traps) is a broad kite shaped muscle that runs from the base of your skull and the tips of the vertebrae out to the collar bone and shoulder blade. The traps help to stabilize and move the shoulder blade, and strong trapezius muscles contributes to improved upper body strength and less risk for shoulder injuries. Many people neglect working the trapezius muscle, but a few simple "trapezius" exercises can make a huge difference in overall upper body strength.
If you ask body builders or power lifters what is the number one exercise for building the traps, most of them will say barbell shrugs, and I agree with them. If you want to build up your traps, you definitely need to include barbell shrugs in your workout. It's an easy move to execute because all you have to do is grab a bar and then shrug your shoulder up towards the ceiling.
Barbell shrugs work on the upper "trapezius", and shrugging motions are the most popular way to work the traps, but you must also work the middle and lower portions of the trapezius. The second great exercise for the traps is bench shrugs. In order to do bench shrugs you must lie on an incline bench with dumbbells in your hands and pinch your shoulder blades back together.
You can do shrugs for the middle traps from a standing position, but it requires that you bend from your waist anywhere from about 45 to 90 degrees. When you are standing, your lower back must stabilize you, but when you lie on a bench the bench stabilizes you. Most people find that it is easier to focus on the traps when lying face down on an inclined bench. The middle traps often get neglected, and bench shrugs are a great way to focus more so on the middle part of the "trapezius".
In addition to barbell shrugs, and bench shrugs, regular dumbbell shrugs are also great for the traps. Dumbbell shrugs are done in a similar fashion to barbell shrugs. Because the dumbbells are much less stable then the barbell, you won't be able to lift as much weight with dumbbells as you will with the barbells.
Some people find that the strength of their traps often exceeds the strength of their grip and forearms, so some people choose to use wrist straps in order to lift more weight. The three exercises above are all great for building the traps, and if you feel like you need to add wrist straps to progress your strength. Try adding some of these exercises into your workout, and you will notice your strength improving.