It's somewhat dated now, but I loved Asimov's Intelligent Man's Guide to Science[1] when I picked it up at a used book sale in junior high. I felt it was great for putting the history of science in context in a way that I never really got from my actual schooling.

Another good one is The Dancing Universe[2], which I got as a textbook for some sort of history/philosophy of science course in undergrad.

[1] https://en.wikipedia.org/wiki/The_Intelligent_Man%27s_Guide_...

[2] http://amzn.to/1Sv6qV7