I like the World Bank site, DOING BUSINESS, which apart from its expressed purpose, is also a useful resource for a quick survey on African economies (the site also covers the other continents). A searchable database provides specific country information (see the drop down menu in the top left hand corner) or subnational data (example, Nigeria). You can ever compare economies by income per capita and population. And it comes with a blog updating new additions to the site. I know some will dismiss it as propaganda for market reform and the exploitation of African raw materials by foreign firms. Which it probably is. But you can not access such a good resource, though. Go forth and search.