Tempso - Finally a place for classical music online!
Metronaut - An app to help you play classical music
musicForProgramming(); - Mixes intended for listening while programming
Flat for Education - The best way to teach music to your students
Music-Map - The Music-Map is the Tourist Map of Music, part of Gnod, the Global Network of Discovery.
Scribd Sheet Music - All the sheet music, books and comics you want for $9/month