Anything by George Gamow! Very entertaining but enlightening at the same time. Plus, his books are very cheap. Just do a quick search on Amazon (note all the extremely high reviews). I recommend:
2) Thirty Years That Shook Physics
3) One Two Three ... Infinity
4) Any of the Mr. Tompkins books
Gamow was one of the top physicists of the 20th century, but had a fantastic sense of humor. His writing is very fun and easy to read, but contains lots of information.
Another suggestion is Understanding Physics by Isaac Asimov (the author of I, Robot).