Even with its vastness, the Internet should not be the only resource when it comes to building circuits. A trip to the library may prove very useful especially when building DIY synths, Opto-Theremins, and other noise circuits. As a regular feature I will begin to provide links to books which I feel would be very helpful to anyone who wishes to start designing and building their own things. The first one speaks for itself. Practical Oscillator Circuits, the main to remember when building audio synths is that the Frequencies have to be roughly between 20Hz – 20kHz anything outside that range will probably not be audible!

Summary:
Practical Oscillator Circuits Manufacturer: Babani
•Complete constructional details provided
•Simple circuits
•Designs using CMOS,timer ICs and op-amps

One of the most frequently used electronic building blocks is the oscillator, and the aim of this book is to provide a rich source of these for enthusiasts to experiment with and perhaps use in their own designs. Extensive coverage is given to circuits using capacitors and resistors to control frequency. Designs using CMOS, timer ICs and op-amps are all described in detail, with a special chapter on waveform generator ICs. Reliable white and pink noise generator circuits are also included. Various circuits using inductors and capacitors are covered, with emphasis on stable low frequency generation. Some of these are amazingly simple, but are still very useful signal sources. Crystal oscillators have their own chapter. Many of the circuits shown use readily available special ICs for simplicity and reliability, and offer several output frequencies. Finally, complete constructional details are given for an audio sinewave generator, which will prove to be a most useful piece of test equipment for any enthusiasts workshop.
Taken from Maplin.com same book for sale there as well.