this book is an overview of everything that was interesting in 70's era modular synthesizers (and therefore, covers 95% of what's interesting with 21st century modular synthesizers). there's a lot to learn here, and while it's a bit of a downer that the example patches are almost all for buchla 200 and/or emu (great for the 50 people that have access to one of those systems) the theory is still applicable to any system, even something like max/msp or csound. i have the second edition in print, not sure it's really worth the going cost. i also can't say for sure whether there's a reason to choose it over the first (which is available online). i can say that it's the definitive book on analog style synthesis and a must-read for anyone who fancies that sort of thing.
This is the Bible of synthesizers programming. Starting from acoustics, physics, electronics and exploiting the modular synthesizer concept to full extent, this book will allow you to clearly understand any synthesizer or sequencer ever built. So full of ideas and techniques you'll never run out of sounds for centuries! Too bad it's out of print. You can try to find an used copy on Amazon but they go for big bucks (over 500US$ for a 2nd edition!!!).
The original modular synth bible. If you patching your own modular beast - you know this book already and it needs no introduction. Apart from the fact that second time I've read the third edition (reprint) and second run of it will be soon on Kickstarter, as far as I know. So if by any chance you've plunged into the modular rabbit hole - get hold of this book and you won't run out of patching ideas for the rest of your life.