I used to prop my mattress upside the wall and punch it like a punching bag. If I just need to head butt, I don't have to prop it on the wall to do that.
Also, it helps to write out what you are feeling...whether in journal form or poetry. You can also attempt painting as I tend find it relaxing and a way to express myself. Art in general is a way to express whatever it is that you are feeling, including anger. I prefer writing and painting, but I'm sure music, theater, dance, etc. all have a similar effect.