Christian Classics Ethereal Library: "The CCEL is a digital library of hundreds of classic Christian books selected for edification and education.”
Religion-online - More than 6,000 articles and chapters by recognized religious scholars. Topics include Old and New Testament, Theology, Ethics, History and Sociology of Religion, Communication and Cultural Studies, Pastoral Care, Counseling, Homiletics, Worship, Missions and Religious Education.
Internet Christian Library: “ICLnet was developed as an archive to support Christian research and ministry. It still contains one of the largest and most complete archive of "classical" Christian materials available on the Internet.”
Google Custom Search of Theological Journals: “Targets over 1,000 Web sites/pages to retrieve full text articles from hundreds of open access journals and other periodicals related to religious studies, scripture studies, systematic theology, practical theology, and cognate disciplines.”
with a unique strength in allows you to search for free scholarly articles, chapters, theses, Some of the websites (e.g., academia.edu) may require you to create a free account in order to download the full text.
Global Digital Library on Theology and Ecumenism - Online digital library of journals, books, and other materials relating to theology, interreligious dialogue, ethics, and ecumenism in World Christianity. Note, you must register for a free account before gaining access to full-text articles.
Directory of Open Access Journals (DOAJ) is "an online directory that indexes and provides access to high quality, open access, peer-reviewed journals." Tip: select "Philosophy, Psychology, Religion" under Browse Subjects to obtain more relevant results.
The Theological Commons is a digital library of 79,332 open access books and periodicals on theology and religion, including 29,730 volumes from the Princeton Theological Seminary Library. The collection spans the period from -1800 to 1926+ and covers subjects such as Protestantism, History, Catholic Church, Church History, and more. Formats include books, periodicals, theses, and manuscripts in multiple languages. The material can be read online, or downloaded in PDF, or sent to Kindle.
Project Gutenberg: The first and largest single collection of free electronic books, or eBooks. Its mission is “to encourage the creation and distribution of eBooks.”
Hathi Trust Digital Libary - Hathi Trust is a partnership of academic & research institutions, offering a collection of millions of titles digitized from libraries around the world. It provides full-text access to millions of books published before 1923.
Internet Archive - "The Internet Archive and Open Library offers over 10,000,000 fully accessible books and texts. There is also a collection of 300,000 modern eBooks that may be borrowed at OpenLibrary.org. " Find out how to Borrow eBooks from Open Library.
Directory of Open Access Books (DOAB) - Provides full-text access to over 1,200 academic peer-reviewed books.