I find John Gribbin very readable, especially in a subject that causes so many people to become terrified. This is the follow on to In Search..., and it is a gem in its own right. How can you go wrong with Einstein explaining Relativity? This is a very brief intro, but it is Einstein...
Feynman is one of those people who looks at the world differently and can make everything clearer. A few people find his different perspective confusing, but most people I know see an amazing beauty in how he describes things. This is his set of text for the intro physics sequence (pretty standard as most use the Berkeley sequence). It has a place in everyone's library, particularly if you have to take the intro physics sequence. This is the accompanying help on problem solving manual. It is worth it. I was given this as a gift several years ago, and what a treat. Feynman reconstructs the motion of planets using only math available 500 years ago. Gives you a lot of respect for Kepler, Newton, etc.
String theory is one of the candidates for a theory of everything, and it truly has a lot of explaining power (largely due to the fact that it is actually a family of theories that with proper selection can explain anything). This is good and bad, but an educated person should be aware of it.. After you read about strings, you should read why some physicists hate it. Since it can be tuned to account for pretty much anything, it makes poor science (how do you falsify it?). This is a detailed account of the problems. Hawking and Penrose... How can you go wrong?!?

Already read those? I generally suggest reading popular math or physics books.

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