Exercise has many benefits, to your health, to your well being, to your psyche and so on. Another study suggests it might help calm you down when you're in an angry mood as well. WebMD has an article entitled, "Exercise May Ward Off Anger" in which an exercise scientists did a small study to see what effects exercise would have on a bad mood.
The small study involved sixteen participants exercising for thirty minutes, and before and after this thirty minutes, participants were shown images known to induce anger, and rate them on a twenty point scale. Participants showed that after exercising and resting the results were slightly different. After exercising, the numbers went down, but after resting, the numbers went up again, showing that exercising might have a chemical reaction toward preventing anger.
There are also thoughts that serotonin levels might be mitigating this change as well. The study is too small to be definitive, of course, but it's interesting to see what the positive affects of exercise can be.