When I am feeling stressed, I notice how tension builds up in my muscles.  Over the years, one of the best methods I have found to reduce this stress (besides getting a massage) is through Focused Muscle Relaxation.

Beginning at your feet, tense up your muscle groups one at a time, holding them tight for 10 seconds, and then releasing for 20 seconds.  Tense up and relax your feet, then your calves, thighs, buttocks, back, stomach, hands, arms, shoulders, neck, and end your face.  Remember to breathe deeply while you are doing this exercise.  This progression will only take about five minutes, and should leave you feeling relaxed and at peace.

Its also a great technique to practice if you are having a hard time falling asleep at night.