Are you familiar with The Robe and other books by author Lloyd C. Douglas? I have been an atheist pretty much as far back as I can even remember, but there was a time in my adolescence when I read almost all of his books. Very well written in my opinion. They almost converted me. Then of course there is Ben Hur available for download right here at Mobileread.

Aside from that I suspect ATDrake's suggestion is excellent and that you will find many places eager to give away such books. The quality of writing might not be the highest though.