"More Guns, Less Crime" by John Lott, Jr.- Senior Professor, Yale University.
It costs about $13 and will really piss off the liberals at the book store. Lott gives an extremely convincing argument for allowing CWP's and an armed citizenry in general. He shatters so many of the myths that are passed on as facts by the liberal media. It is truly one of the greatest weapons to have in one's pro-gun arsenal and will make anyone with an open mind think twice about "gun control." Look for the 2nd edition, which was published last year, in paperback for around 13 bucks.
If your local store doesn't have it- ASK- this book should be shown to every pinko gun grabbing asshole who thinks that disarmament saves lives. Lott shows that, in reality, gun control costs many more people their lives- something you'll never hear from Dan Ratherbiased. Read it, you won't be sorry!
One caveat, however: the book can be quite technical and academic at times, but skim through all of the technical mumbo jumbo if you aren't the academic type. Lott has more statistics than I can type, but there is some priceless information in there.