An international team led by Sarah Tishkoff, in collaboration with our own Scott Williams, and former CHGR member Jason Moore, published yesterday in Science the largest, most comprehensive characterization of genetic variation in over 100 different African populations. The graphic below summarizes some of this regional variation by displaying the proportion of each of 14 color-coded ancestral populations that are found in modern African subpopulations.
UPDATE 2009-05-01: I didn't read through the 100+ page supplement with 40+ figures, but this has made quite a splash in the popular science journalism press. You can read about the highlights here, here, here, here, here, here, here, and here.
Science: The Genetic Structure and History of Africans and African Americans