Grove Music online is our primary music eReference tool, and it includes a lot of information on world music. Keep searches simple, and look for the broader categories that discuss your topic.
A great print encyclopedia on world music, where you can find substantial essays on the traditional music of a nation you are researching. Expect them to be longer than an article but shorter than a book.
Multi-volume encyclopedia that focuses on global popular music. The first two volumes give a breakdown of the industry and instrumental areas. The rest of the set contains 2 volumes on each continent, one with essays broken down by nation/region/city, and the other by musical genre.
The Garland Encyclopedia of World Music by 
Continuum Encyclopedia of Popular Music of the World by 
International Encyclopedia of Dance by 
