A comprehensive collection of classical music available online. While listening, you can read notes on the works being played as well as biographical information on composers or artists in Naxos's extensive database.
Looking for journal articles? Try these databases first.
Grove Music Online is an encyclopedia that comprises the full text of The New Grove Dictionary of Music and Musicians, 2nd edition(2001), The New Grove Dictionary of Opera (1992), and The New Grove Dictionary of Jazz, 2nd edition, (2002).