For a limited time, Christian publisher Crossway has made all of their e-books available from their site for $5.99.
http://www.crossway.org/blog/2012/01...ebook-special/
Though the complete list is too long to include here, I'll point out that this special also includes the bestselling ESV Study Bible and MacArthur Study Bible.
http://www.crossway.org/books/esv-study-bible-ebook/
http://www.crossway.org/books/the-ma...y-bible-ebook/