Well... anger is something I've dealt with for many years. And often, like you, it wasn't really directed at anyone or anything in particular. I was just pissed! What I always found to be the most effective was simply hard physical labor. Years ago, my favorite outlet was chopping wood!

Here's a link to DocJohn's article on anger management, from PC's archives. The article provides links to a number of additional articles on the subject as well:

Anger Management & Coping with Angry Feelings - Psych Central