If you're not scaring off running backs or shirt salesmen with the size of your neck, it's because you're working only the uppermost part of your trapezius muscles, which extend from your spine to each shoulder, across your upper back.
To build better traps, you need to work the middle and lower parts of the muscles, too. This is a list of some of the best exercises to make your traps as big as possible.
Overhead Machine Press
Adjust the seat so that you can grasp the resistance handles at shoulder level. Inhale and push until you arms are fully extended. EXHALE as you return to the starting position, and repeat.
Seated Cable Row
Sit at a cable-row machine. With your back straight and knees slightly bent, extend your arms and hold the bar. Squeeze your shoulder blades together and hold for one count to isolate the traps. Then pull the bar toward your gut, and return to the starting position.
Dumbbell Shrug
Stand with your feet slightly apart, holding a dumbbell in each hand, and bend forward at your waist about 10 degrees. Shrug your shoulders up and slightly back toward the base of your skull. Then return to then starting position.