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
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.)
The North American Patristics Society has a wonderful page of internet resources.
Tertullian.org – tons of church fathers!
Horton Davies – The Worship of the English Puritans
Charles Garside, Jr. – Zwingli and the Arts
James Hastings Nichols – Corporate Worship in the Reformed Tradition
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
Larry Sibley – The Legacy of the Geneva Liturgy
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)