The New York Philharmonic has a great collection of historic scores and programs available online.
A Traditional Music Library has an extensive collection of lyrics, how-to links, scores, and much much more of music traditions from around the world.
MuseData has printable scores from many of the major classical composers.
Chicago Symphony Orchestra
Lyric Opera of Chicago
New Music Chicago
AllMusic is an online database that has detailed information on musicians, composers, recordings throughout history.
Pandora is a online streaming audio website that allows users to create stations based on artists, songs, or genres. A good way to sample some of the music you are studying.