The Classical Archives is the largest classical music site on the web: 40,055 full length classical music files by 2,093 composers.

MacMusic is a huge community of audio professionals, motivated by the wide possibilities, offered by Macintosh computers to create music

The MIDI Basics page from TweakHeads Electronic Musicians Cafe. Has a good overview of MIDI, but also a sidebar to information on many other music technologies.

The purpose of the Vermont MIDI Project is to encourage and support students in composing and arranging music. A community of professional composers, teachers, pre-service educators, and students engage in mentoring and online discussion of student work