Breathing exercises, any kind of exerting activity can help burn away some of that anger.

Slipping up happens and it's best to live day by day, see how far you can go without cutting and consider every new day an accomplishment. But if you ever cut again, don't beat yourself up, just try to figure out something different to do.

It seems that you cut when you are angry or upset, so it's an emotional release for you, like it is many people. I think venting your anger would be the best strategy to try. By doing what puzzclar said or by finding some physical activity to do like soccer or something that you enjoy.