Britannica Middle School:
Classical music
Country music
Folk music
Hip-Hop
Jazz
Popular music (Pop)
Rhythm and blues
Rock
All Music (website):
Classical
Country
Folk
Jazz
Pop/Rock
R&B
Music Genres List (website):
Classical
Country
Folk (aka Singer/Songwriter)
Hip-Hop
Jazz
Pop
R&B/Soul
Rock
Other websites:
Shine Music School: The History of Pop Music
Shine Music School: Jazz vs. Classical Music
MTV Music Evolution: A Brief History of Hip-Hop
E-books (search for your genre)