Try this guide:
World Music - The Rough Guide
Got this as a text book while taking a world music class at UCSD. Obviously it is not comprehensive, being only one (thick) book but it does covers major (traditional) world music artists and the history of the culture/music. The class was great, got to see Ladysmith Black Mambazo, and Zap Mama live because of it. Both not mentioned in this thread yet. Got turned to Baba Maal, Khaled, Apache Indian, Oumou Sangaré, and all sorts of stuff from it.