This exercise works the triceps, particularly the long inner head of the triceps. 
Grab a dumbbell with one hand. Stand with your feet shoulder width apart. Lift the dumbbell so that it is at arms length straight above you shoulder. Keep a slight bend in your knees to take pressure off the lower back.

Lower the dumbbell in an arc motion behind your head Triceps Workout until your elbow is at a 90-degree angle. Lift the dumbbell in an arc motion back to the starting position. Repeat for the desired number of reps. Do the same for the other arm.

Tip - You can do this exercise with both arms at the same time by using a barbell, two dumbbells, or holding 1 dumbbell with two hands. 
 

Tricep Push Downs

This exercise targets the triceps, particularly the outer head of the triceps. 
Attach a bar to an overhead pulley. Stand in front of the pulley with your feet shoulder width apart. Grab the bar with a narrow overhand grip. Bend your arms fully and tuck your elbows close to your sides at all times during the exercise.

Moving just your forearms push the bar down in an arc motion until your arms are straight. Hold this position and squeeze your triceps for a second to maximize the peak contraction. Slowly Hamstring Exercises lower to the starting position. Repeat.

Tips - do not let the weight plates touch during the exercise, keep the tension on the tricep muscles. For variety you can use different bars attached to the overhead pulley (i.e. rope, ez bar, V bar, etc.) to work the muscles at different angles.

Tricep Dumbbell Kick Backs

This is a good exercise to hit all three heads of the triceps with a good peak contraction. 
Brace yourself against a flat exercise bench. Grab a light dumbbell in one hand. Place your other hand on the bench to support yourself.

Keep your upper arm along the side of your torso during the entire exercise. Moving just your forearm lift the dumbbell in an arc motion until your arm is straight. Hold this position for a couple of seconds to maximize the peak contraction in the triceps. Slowly return the dumbbell to the starting position. Repeat.