HathiTrust
HathiTrust contains the searchable full text of 3.2 million books (and growing). The bulk of the full-text content consists of books published prior to 1924, though some newer full-text books are available as well. All full-text books can be viewed online (free), downloaded in .pdf format (free), or ordered in paperback format (prices vary). HathiTrust also permits full-text searching of millions of in-copyright books, though these books cannot be viewed as full text, downloaded, or purchased directly from the HathiTrust website.

HathiTrust “is a partnership of major research institutions and libraries working to ensure that the cultural record is preserved and accessible long into the future. There are more than 80 partners [as of 2014] in HathiTrust, and membership is open to institutions worldwide.”