Early Music: The Instruments of Early Music

A wide array of free resources that covers databases, finding scores and sources, periodicals, recordings, period instruments, societies, and information on notation and theory.

Instruments

CWRU Early Instrument Database, by Ross W. Duffin
It contains sound files, illustrations, and brief essays about Medieval, Renaissance, and Baroque musical instruments.
A Guide to Medieval and Renaissance Instruments
Sound and video clips of Medieval and Renaissance instruments being played. (not MIDI files).