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IMSLP

The largest sheet music archive in the world. Contains about 80000 scores and small amount of audio.
Jazyky:  English  
Koncovky:  

Boxset

Lossless classic. Very big archive.
Jazyky:  English  
Koncovky:  

Kunstderfuge

The world largest collection of classical midi music
Jazyky:  English  
Koncovky:  

Arcadiy Chubric's mp3 archive

About 80 hours of classical music played by site autor and others
Jazyky:  Русский  
Koncovky:  

Art of piano

Piano mp3 and articles about famous pianists
Jazyky:  Русский  
Koncovky:  piano

Skripach.ru

Russian site about violin. Violinist biographies, mp3, backing tracks.
Jazyky:  Русский  
Koncovky:  скрипка

Intoclassics

Classical music. Audio and Video.
Jazyky:  Русский  
Koncovky:  

Alexander Nevilo's library

Sheet music and mp3 of classical music.
Jazyky:  Русский  
Koncovky:  

Fagotizm

Bossoon sheet music, mp3, links, forum
Jazyky:  Русский  
Koncovky:  bassoon