Early Music: Renaissance

A Performer's Guide to Renaissance music, edited by Jeffery Kite-Powell is an excellent primer for performing this repertoire  
Music in the Renaissance, by Howard Mayer Brown provides a very readable overview of the music and composers of this era  
Gustav Reese's Music in the Renaissance is a more in-depth history of this musical period
The Performance of 16th-century music: learning from the theorists, by Anne Smith is almost indispensable for performers trained in the practices of later music who wish to perform earlier repertoire.

An Anthology of early Renaissance music, ed. by Noah Greenberg and Paul Maynard
Historical sets, collected editions, and monuments of music : a guide to their contents, compiled by Anna Harriet Heyer provides access to the many works in anthologies, etc
A Shakespeare music catalogue by Bryan N.S. Gooch, and David Thatcher in four volumes lists all music associated with Shakespeare and his plays 
Music in Medieval and Renaissance Life ed. by Andrew Collier Minor
Early Music Online from the Royal Holloway University of London 

Josquin des Prez : Missa Pange lingua : Tallis Scholars, Peter Phillips, cond. available online  and CD
Claudio Monteverdi : Madrigali guerrieri et amorosi : The Consort of Musicke, Anthony Rooley, cond. available online  or selections on CD
Palestrina : Missa Papae Marchelli : Choir of Westminster Cathedral, David Hill, cond. available online  
Victoria : Motet O Quam gloriosum : Choir of Westminster Cathedral, David Hill, cond. available online   and on CD
William Byrd : The complete keyboard music of Willliam Byrd : Davitt Moroney, keyboards