This website does not just offer Imperialism of Asia, it compares Imperialism and its effects on Brazil, South Africa, China, and Japan. It goes through the history of each, why it occurred and the results of colonialism. They offer lesson plans, supplementary reading for the students, videos, and pictures that relate. The video that they have attached to it is 28 minutes and compares the colonial imperialism of these places and explains some key components to this time period, like the Meiji Restoration, the Boxer Rebellion, and the Opium Wars. This video would be a great introduction to an imperialism unit. This website is funded by the Annenberg foundation and is completely free and they don't make you sign up for anything either. I would recommend this website for World History Teachers.
http://www.learner.org/courses/worldhistory/unit_overview_20.html