When you look at articles in reference books, make sure you note the following: alternate names for the ethnic group ("ethnonym"); alternate spellings of these names, where the group lives, name(s) of the group's language. All these things can help you find more information later. Also note any bibliographic references to books or articles about the group.
The Encyclopedia of World Cultures by 
International Encyclopedia of Social Sciences (2008)
Dictionary of Anthropology by 
Folklore: An Encyclopedia of Beliefs, Customs, Tales, Music, and Art by 
The Greenwood Encyclopedia of World Folklore and Folklife by 
Encyclopedia of Cultural Anthropology by 
African Mythology A to Z by 
Encyclopedia of Death and the Human Experience by 
Cultural Encyclopedia of the Body by 
Encyclopedia of Multicultural Psychology by 
Tobacco in History and Society: An Encyclopedia
Worldmark Encyclopedia of Cultures and Daily Life
Encyclopedia of Anthropology by 
Icons of Evolution: an Encyclopedia of People, Evidence, and Controversies by 
