Center for the Study of Political Graphics has a huge collection with over 50,000 posters, the largest collection of Post World War II graphics in the US. The Center for the Study of Political Graphics collects, preserves, and exhibits posters relating to historical and contemporary movements for social change. They also organize travelling exhbitions by themes like ecology, labor movement, black panther party USA, human rights, political prisioners, sexism and homophobia, international women's liberation, the war against children, and more. (via El Burlador)