A series of studies by Dutch researchers examines the effect anger has on people's problem solving skills, and finds that angry people produce a higher volume of ideas, as well as more creative ones than their non-angry counterparts. The study's authors reason that anger is usually accompanied by a feeling of intense energy and a less-structured style of thinking, two factors that lead to creative forms of brainstorming.
That burst of productivity however is short-lived and ultimately creativity is reduced as a result. The authors found that anger leads to initially higher levels of creativity than sadness, but that anger depletes resources more. As a result creative performance declines over time more for angry people than sad ones.
So, if it's your job to be creative for long periods of time, better to be sad than angry. But if all you need are short bursts of sporadic creativity, rage away.