Best single volume guide to classical music

If you are looking for recommendations for not just pieces, but good recordings of those pieces, I recommend “1,001 Classical Records You Must Hear Before You Die.”  It is organized chronologically by date of composition and covers early, pre-renaissance to 21st century music.  I like the examples chosen for each era and the specific recordings are also quite good.  The balance of selections-between large scale, chamber, solo, choral and vocal works is reasonable.

For a survey that is about composers and their works, and not about recordings, I would recommend "A History of Western Music" by Burkholder.  Another classic is "The Lives of the Great Composers" by Schonberg.

The ultimate book source of information on music is the New Groves Dictionary of Music it is a fairly large encyclopedia with topics arranged alphabetically.   Even very old sets are north of $500 and it does take up a lot of room.  It is fun to browse if you have an interest in music, but, it is primarily a tool for very serious students.

The Penguin Guide is pretty good for choosing specific recordings, but is not that great a guide for determining which specific piece is significant or a good introduction to a particular composer or type of music. It is unfortunate that the Penguin Guide has not been updated for more that a dozen years or so.  But, some other people have used the Penguin ratings for identifying the better recordings that can be bought from their site.  The very best recordings that are contained in the Penguin Guide earn a "Rosette."  You can find lists of Rosette winners by googling Penguin rosette.  This particular website has Rosette winners categorized by different musical eras which is quite helpful: