Pardon me if I missed any previous mention of these books while scrolling through the thread:

I can highly recommend Alex Ross's book The Rest Is Noise, published last year. It's a survey of 20th Century music written with such insight and enthusiasm that I felt compelled to get a recording and listen to each composition that he discusses. This book has actually influenced my listening and appreciation of music,

J.W.N. Sullivan's Beethoven is an old classic that contains one of the most profound discussions of meaning in music that I have ever encountered.

Paul Griffiths' Concise History of Western Music gives the big picture in less than 350 pages. Published by Cambridge U Press, it got some nice reviews last year, which is why I bought it. Might be a good place to start before delving in more detailed histories.