General starting places are: the Early Music FAQ, which provides
information and answers as well as useful links
the Early Music Institute's home page, part of the Indiana University School of Music
Voice of Shuttle's links to early music pages and
the Early Music Network, offering "[i]nformation and services about early music and historical performance all over the world"
For specifically English
early music, go to Early English
Musick: 1385-1714, which includes information on composers and their
works as well as a very full bibliography.
Another resource with an English focus is Richard Rastall's thesis, Secular Musicians In Late Medieval England. There are three links to follow at the moment: one for the preface, a second for volume 1, and the last for volume 2.
Mediaeval Music Database at LaTrobe University Library in Australia offers "a systematic collection of scores, colour images, texts and bibliographic information of medieval music which can be searched by text or melody and
which will return musical information in the form of a modern score, text
data and, where available, a colour facsimile of an original manuscript"
as well as "a complete annual cycle of liturgical chant taken from
original medieval sources and complete works of selected composers from
the twelfth to the fifteenth centuries".
Resources for chant can be found at:
The Monumenta Musicae
Byzantinae, Copenhagen for Byzantine chant and
The Gregorian Chant Homepage for Western chant.
Secular singing is the focus for Sixteenth Century Ballads .
Focussing on instrumental music of the period is A Guide to Medieval and Renaissance Instruments, a site with information on the musical instruments of the period, as well as links to other sites dealing with specific instruments.
Other sites with a focus on early musical instruments are A Guide to Medieval and
Renaissance Instruments and Renaissance Instruments.