AllMusic - This is an open-access online database with information about genres and artists.
American Popular Music (Ebook) by Larry Starr and Christopher Waterman - This is an ebook with sections on the history of various musical genres.
Library of Congress - Celebrates the Songs of America - This collections of articles and essays provides information on historical topics, musical styles, and more. It also includes a timeline showing the link between songs and cultural/historical events and artist biographies.
NPR Music - Search this site for information on artists, genres, and other music news.
Rock & Roll Hall of Fame Research Guides - Scroll down this research guide made by the librarians at the Rock & Roll Hall of Fame for guides about artists, genres, recording studios, & exhibits.