Wikipedia: Musical Genre - Brief explanation of the way styles can be defined by region, chronology, technical requirements, marketing trends, or the ideas of critics. Extensively linked to sub-genres and examples of significant artists. - http://en.wikipedia.org/wiki/Musical_genre
Full Throttle Music - Focus on contemporary popular music. Features reviews of CDs, movies and products and includes interviews. - http://www.fullthrottlemusic.com
History of Country Music - A chronological review of artists and songs from 1920 to 2000. Includes archive images, sound clips and movies. - http://www.roughstock.com/history/
Music Genre Sampler @ DataDragon - Learn about different musical genres including rock, Celtic, and classical. Includes information about artist and site links. - http://datadragon.com/education/genres/