ABZU--Ancient Near East Texts on the Web
Includes primary texts digitized for the ETANA (Electronic Texts and Ancient Near Eastern Archives) project.

BibleGateway.com: the Bible in Over 100 Versions
A concordance to multiple Bible versions, including the KJV and the NIV.

Online Bible Study Tools (includes NRSV and Douay-Rheims Bibles)
Includes a basic commentary, as well as concordances to multiple Bible versions, such as NRSV and Douay-Rheims.

Christian Classics Ethereal Library
A full text collection of classic texts from the church fathers to the nineteenth century.

Google Books
Includes full views of books in the public domain, and limited previews of select books.

HathiTrust Digital Library
This collection of books from university libraries includes many full text works in the public domain.

Internet Archive Digital Library
A freely available library of texts, audio and video.

Online Books Page from UPenn
A guide to freely available full text books.