History

General

William D. Maxwell – An Outline of Christian Worship: Its Developments and Forms (A classic work, though somewhat dated.  Maxwell was Scottish Presbyterian who tried to restore the richness of Reformed catholic worship.)

Jaroslav Pelikan – Credo (the new standard text in creedal/confessional history)

Bard Thompson – Liturgies of the Western Church

James F. White - A Brief History of Christian Worship

•  Protestant Worship: Traditions in Transition

Geoffrey Wainwright and Karen B. Westerfield Tucker (eds.) – The Oxford History of Christian Worship.  (The new standard work.  Corrects and refines many earlier theories of liturgical development.)

Patristics

The North American Patristics Society has a wonderful page of internet resources.

Tertullian.org - tons of church fathers!

Reformation

Horton Davies – The Worship of the English Puritans

Charles Garside, Jr. – Zwingli and the Arts

James Hastings Nichols – Corporate Worship in the Reformed Tradition

The Westminster Assembly Project

Books 

John Calvin – The Necessity of Reforming the Church [on-line version] (brief defense of the Reformation)

Hughes Oliphant Old – The Shaping of the Reformed Baptismal Rite in the Sixteenth Century 

Jaroslav Pelikan – Obedient Rebels: Catholic Substance and Protestant Principle in Luther’s Reformation

Articles 

Larry Sibley – The Legacy of the Geneva Liturgy

Modern

D.G. Hart –  John Williamson Nevin: High Church Calvinist (useful to understanding how one can be both “reformed” & “catholic” but also helpful in studying Nevin’s mistakes).  See also Nick Neeham’s brief review of Nevin’s Anxious Bench.

Thomas Oden – Requiem: A Lament in Three Movements (helpful in understanding the plight of the modern church)