I’ve recently just finished reading Packt Publishing’s book Instant Audio Processing with Web Audio by Chris Khoo.
As the API is relatively new and is currently being standardized, it is harder to come across a variety of useful examples to get started with. This book can get you up and running with many shorter code examples all set up with HTML/CSS. Overall it is a relatively short book at 76 pages, but provides a bonus section for download including another 26 pages of material.
Overall this book is a good place to refer to for more in-depth examples when learning the API and reading Web Audio’s working draft.