The best African-centered teaching materials and resources come from universities, and all of them have "Outreach Centers" which provide information and resources to teachers. This is the best way to go if you're starting from scratch. They have manuals, books, videos, etc., and provide LOADS of resources. Once you go this route, you'll be addicted.
The key to teaching Africa effectively, since it is so large is to pick critical content you want to convey to your students, and build a unit around that, otherwise you'll find yourself lost in a forest of resources about every facet of this enormous, highly diverse continent.
Some content to consider:
1) Select several ethnic groups from different countries - or all from the same country- and have the students compare and contrast the research they do on their cultures.
3) Study one of the 53 countries- If you're going this route, Nigeria has all the major land forms which present themselves in Africa. It also contains over 250 ethnic groups (the most predominant of which are the Muslim Hausa and Fulani from the North, and the Igbo, and Yoruba from the Christian South) who speak over 500 languages. (This is why it is impossible to teach ALL of Africa.)
* See the list of African Studies Outreach Centers on the next page.