I discovered christianaudio.com this weekend. It's a great site with many books available for download (for a price), and also lots of free interviews with amazing authors like Dallas Willard and Brian McLaren. If you are in love with your iPod like I am, you may enjoy some of these.
I also got a promotion code for a free download of Thomas A Kempis' Imitation of Christ. Just choose to download that book, and then type in FREEIMITATION for the promotion code.