Classical

American Mavericks - Streaming audio of works by 20th century American composers, including Cage, Cowell, Adams, Babbit, and Copland.
musicmavericks.publicradio.org/listening/

Classical Archives - Includes thousands of files (MIDI, MP3, and Windows Media Audio) from over 1000 composers.
www.classicalarchives.com/

Classical Piano Midi Page - Includes over 40 MP3 files of classical piano music realized by Bernd Krueger.
piano-midi.de/midicoll.htm

Classical Piano Short Pieces - MP3 and MIDI recordings of sequenced performances.
pianomidi.org/

ELIXIR's MIDI Page for Classical Guitar - MP3 sequences; MIDIs fine-tuned to Roland Sound Canvas SC-88. [Japanese/English].
www.guitarsound.net/elixir/

Ian Partridge, Tenor - A few audio and video tracks by Tchaikovsky, Schubert, and Ivor Gurney.
www.ianpartridge.pwp.blueyonder.co.uk/audio.html

J.S. Bach Organ Music - Numerous works performed by various organists on the grand Marbella Organ in Spain.
www.johann-sebastian-bach.org/

Karadar Bertoldi Ensemble - Popular classical selections in MP3 and MIDI formats.
www.karadar.it

Kunst der Fuge - Thousands of free classical music files (MIDI, MP3, WMA, Real) of fugues and other contrapuntal music.
www.kunstderfuge.com/

Limburg Cathedral Boyschoir - Choral music by Mozart, Mendelssohn-Bartholdy, Rutter, and Rheinberger.
www.limburger-domsingknaben.org/english/mp3.htm

Lisztonian - Classical piano music performed by Jeremiah K. Jones.
www.lisztonian.com

Mackay-Smith Index - Catalogue of instrumental music includes classical MIDI and WAV files.
www.lib.virginia.edu/dmmc/Music/MackaySmith/

Michael's Classical Piano Site - MP3 and MIDI files of classical piano music.
www.88-keys.com/

Musical Selections - Classical piano music by a wide variety of composers.
www.musicalselections.com

Opus100 - Streaming RealAudio excerpts of many classical works.
opus100.free.fr/

Russian Art Songs - MP3 and RealAudio selections from several centuries of Russian vocal chamber music.
www.classicalmusic.spb.ru/music-mp3/

Steve Sycamore - Original 21st century art music in MP3 and MIDI format.
sycamore.inr.net/music

SuperConductor - Classical music performances created with SuperConductor software.
www.superconductor.com/mp3.htm

Tubalate - Tuba and euphonium quartet shares RealAudio excerpts from their CDs.
www.dwsolo.com/tubalate.htm

Wikipedia - List of free classical music recordings, mostly in ogg format, available at Wikipedia.
en.wikipedia.org/wiki/Wikipedia:Sound/list