Brief Answers to the Big Questions is a wonderful collection of the late Stephen Hawking's musings on the "Big Questions". Not everyone will agree with all of his views, but it's difficult not to be inspired by the cosmic journey Hawking transports you through, and the heartfelt optimism he has for the future of humanity.
Why Relativity is Right
One of the most common headlines I see in popular science articles is "Was Einstein Wrong?". While it is certainly true that relativity is going to be replaced by some more advanced theory of physics at some stage, the basis of Einstein's theory is unlikely to change.
What do Theoretical Physicists Do?
To anyone who is confused about what it is exactly that theoretical physicists do, here is a brief yet broad summary of what we're trying to achieve.
Do Space and Time Really Exist?
There is a split in the philosophical community with regards to this issue. By and large, the majority of philosophers of physics claim that space and time are real and important entities, but there is a small faction who maintain that space and time are just useful theoretical constructs that don't have the independent existence we sometimes attribute to them.
Why Relativity Has Nothing To Do With The Speed of Light
We can get most of the way to deriving the constancy of the speed of light just from the Principle of Relativity alone. In other words, the speed of light being constant is just a consequence of the laws of physics being the same in all inertial frames.
Black Hole Fun
If it's possible to have a favourite astronomical object, I'm sure black holes would be fairly high on everyone's list. You can't escape from one, you can't know what's inside one, and they're invisible - what could possibly be more terrifying and exciting to talk about?