Here are some links that were very useful for me:
Tammo Hinrichs "kb" of demo-group Farbrausch articles about audio programming.
There is also a video of a seminar that Tammo held over here.
Jari Kleimola masters thesis "Design and Implementation of a Software Sound Synthesizer".
Over 100 pages about audio programming.
The Synthesis ToolKit in C++.
A advanced audio toolkit developed at universities.
Main author of the toolkit is Perry Cook who has also written a book: "Real Sound Synthesis for Interactive Applications".
"Basic sound theory and synthesis" article by Dr Petter.