There have been a few books out of the 90 or so authors we have had on that bought and gave around to family etc. All of our authors are great (we have them on for a reason, afterall) but we each have different tastes and the following especially appealed to me:
Druyan/Sagan (gave a copy of this to a woman sitting next to me on a flight after a beautiful conversation, and then had to go get other copies for me and my friends and family. This was a great introduction to these topics for my mother—I did the same years ago with Demon Haunted World. Books are powerful ways to evangelize.)
Dawkins, of course
I also gave Peter Irons’ God on Trial to old friends of mine from bible college who seemed to dismiss the justifications those who work for church state separation give.
As for the other books— I really wish everyone involved with the humanist and atheist movement would read Kitcher’s Living with Darwin. He speaks directly to the issues that ostensibly get us organizing and working together, and I found him very persuasive.
And of course Hitchens and Harris are great books to give the relatives who want to see why you’re such a loyalist to the atheist cause.