"Early Music" is generally considered to be music written in the Baroque period or earlier (i.e., prior to about 1750). There are enough sites which specialize in topics related to music of the Medieval, Renaissance, and Baroque periods to warrant a dedicated page of links, though it should be remembered that sites listed on other link pages also have significant amounts of information pertinent to early music as well.
Todd McComb's
Bruno Cornec's
Brad Leissa's
Also see Festivals, Concerts & Competitions
Also see Societies & Organizations