Is there a piece of classical music that you desperately want to hear? you'll find it at Naxos.www.bbc.co.uk/radio3/discoveringmusic/audioarchive.shtml
BBC Discovering Music Archive: An excellent resource for beginners and experienced listeners alike, with illustrated audio talks on a wide range of composers and pieces.
Columbia University Music Reserves, the selection is limited, but the recordings are excellent.http://www.archive.org/
Contains massive amounts of documents, videos, and audio, although the quality is somewhat questionable.http://classical.com
not as good as Naxos, but decent enough to deserve a mention.Sheetmusicwww.dlib.indiana.edu/variations/scores/
Looking for the scores of Bruckner's 9th? you'll find it here.www.imslp.org
Looking for free scores?Biographies/Music LearningWikipedia.com
A good place to read about composers that you don't know. Wikipedia has very good biographies and links.www.musictheory.net
A good place to learn the basics of music theory, the first step of becoming a composer.www.grovemusic.com
a website to find biographies on composers, however, Wikipedia actually contains more informations on composers than this site.