Books on Classical Music in the Public Domain

[Opus106]

It would probably take me a couple of seconds to search for and few more minutes to sift through the results at Project Gutenberg or Google Books to find some, but I'm looking for recommendations of good ones that you may have read or are considering to read. At present I prefer those works which can be read and appreciated by the (music-wise) technically-challenged; however, let us know about all your favourites.

I thank you in advance.