A Universe from Nothing
Interesting, easy to read, but probably won't convince those who have already decided the answer is 'God'. Obviously, doesn't definitively answer why there is, in fact, something rather than nothing, but does a good job of explaining space/time, inflation, anthropic principle etc in a non technical way. For a more detailed look at this kind of thing check out http://www.goodreads.com/book/show/771550.The_Cosmic_Landscape
