One of the best books I have read is Francis Chan's "Crazy Love". It is one of the first books I recommend to people who want to understand more about the Gospel and its' implications on a believer's life.
Christianaudio.com is for the month of July offering the Audiobook version for free. I cannot tell you how highly I recommend downloading this and listening to it.
Click Here to go download this Audiobook and also sign up for thier newsletter, as they offer a free audiobook every month and usually the books are really legit.