New eBook Reader from Adobe
I highly recommend you download Adobe's relatively new ebook reader: Adobe - Digital Editions. It makes reading pdf ebooks very easy on the eyes. I used to hate reading ebooks in pdf format because it was somewhat cumbersome. Now that I've been using Adobe Digital Editions, I find myself preferring to read pdf copies to physical copies.
DesiringGod has released some of Pipers books and other resources for free in pdf format, Sovereign Grace has many pdf resources, and Crossway often will send you a pdf copy of a book if you purchase it directly from them (usually a little more expensive though).
Make Careful Choice of the Books Which You Read
Don Piper makes the list, John Piper doesn't. A look over the top 50 Christian authors gives a good indication of what Christians are reading. I can't help but to call to mind the Spanish dicho (saying): Por eso estamos como estamos (That's why we are how we are).
Reflecting on this list also reminds me of a Richard Baxter quote I recently read on Challies.com:
“Make careful choice of the books which you read: let the holy scriptures ever have the pre-eminence, and, next to them, those solid, lively, heavenly treatises which best expound and apply the scriptures, and next, credible histories, especially of the Church … but take heed of false teachers who would corrupt your understandings.”
Challies comments with discernment:
For every good book, there are five or ten (or, more likely, far more) that are fit only for the trash. Much of what is published under the banner of “Christian” is anything but. Be careful what you read, for a book can lead you astray as easily as it can lead you closer to the Lord. Find mature believers who can guide you to books and authors that will edify you.