Christian Classics Ethereal Library (http://www.ccel.org/) is a collection of classic Christian literature that is available for free online. This site can be searched by topic, by title, by author, or by keywords anywhere in the book. Once an item is selected, it can be read online, read on a mobile device, or downloaded.
Princeton Theological Commons
Princeton Theological Commons (http://commons.ptsem.edu/) is a digital library of over 80,000 resources on theology and religion. It consists mainly of public domain books but also includes periodicals, audio recordings, and other formats. You can narrow results by date ranges. You can read it online, get a PDF, or copy it to Kindle. The online format allows you to search within the text for keywords and phrases and will mark the pages along a line at the bottom of the document.
