There have been lots of lovely suggestions for using rocks to ground excess anger. With all of the discussion of various types of rocks and how best to attune yourself to them, the bottom line is that if you have a lot of excess anger, the first thing you should be doing is grounding. And as much as I love my rocks, there are other things you can do as well.
A daily mini-meditation is crucial for me to keep myself in check. I try to give myself 5 minute breaks throughout the day, whenever I feel like I'm getting overwhelmed by things. I sit quietly with my eyes closed, and breathe deeply up through my feet and through the top of my head. If I can't just sit somewhere, I try to take 5 minutes and walk briskly or do something else that completely engages me physically. This helps dispel a lot of the jittery feeling that anxiety can bring on. A longer meditation (20-30 minutes) is helpful on a daily basis, if your anger is sustained over a period of days, weeks or longer. This meditation can be of any variety, but you should try to touch base with yourself at least once a day.
These techniques aren't just for anger, but any excessive, distressing emotions. Meditation helps you stay focused and grounded, and makes you less likely to feel overwhelmed by the world.
~Flame RavenHawk