Resources for MIDI

General

1. http://www.midi.org
Homepage of the MIDI Manufacturers Association, who maintain the official MIDI specification.

Data Format

2. http://improv.sapp.org/doc/misc/MidiFileFormat.html
Short but complete description of the Standard MIDI file format.

Musical Data

3. http://www.prs.net/midi.html#index
The Classical Music [MIDI] Archives