I heartily agree with the Rough Guide music series.
But you should start with The Rough Guide books on World Music. There are 2 volumes and are probably the definitive road map to the genre of World Music. Every country and style of music is covered. Each section has some interesting recommendations to get you on your way.
here's a link
http://www.roughguides.com/music/
Final note: Rough Guide has a bunch of other books on different styles of music like Rock, Classical, Opera, Country and Jazz.
Peace, Rick
NP: World Without Tears, Lucinda Williams