If you haven't seen it yet, his most recent show on the Discovery channel is incredible. It includes a lot from his previous writings but some new stuff too and it's all set to pretty stunning effects and a great soundtrack reminiscent of scifi movies from the 70s and 80s. You can check it out here:
His discussions and examples for why we wont be able to travel back in time are perfect for explaining the concept for people. He manages to communicate such high level stuff in such a great way on that show (well, always, but the show is much more approachable to the masses).
http://dsc.discovery.com/tv/stephen-hawking/
and the whole series is on netflix. It's truly amazing. Don't miss it.